Welcome to Evil Mart

Here, you can find all of the delightfully vile tools you could ever need as a Big Bad. Need a Death Trap? We carry them all, from Acid Pools to Trap Doors! Looking to make your Mooks more reliable? You can trade in the standard issue variety for top-of-the-line Evil, Inc.. Mecha-Mooks! Want to build a new Supervillain Lair or Den of Iniquity? We offer not only the materials, but some of the finest dark and foreboding real estate around!

So, what will it be today?

Not to be confused with Predatory Business, which is about corporations that are seen as evil due to unsavory business practices.

Examples of Welcome to Evil Mart include:

Comic Books

Several Marvel villains made careers out of this: Arcade used to make money by producing robotic "heroes" for the villains to practice on while Taskmaster made money by providing training for Mooks.
Justin Hammer and the Tinkerer are well-known super-villain technology suppliers in Marvel.
One of Spider-Man's less formidable enemies, the Kangaroo, got a suit of Powered Armor from the "Sharper Villain's Catalogue", but given its quality, the place is likely a scam.
Leo Zelinsky is a tailor in Brooklyn who makes costumes for the heroes and villains in Marvel, though he alternates days, opening his shop for bad guys on Saturdays, Tuesdays and Thursdays, and for heroes on Mondays, Wednesdays, and Fridays. He sees nothing wrong with this - he's just a guy trying to make a living.
In the comic book adaptation Gravity Falls: Lost Legends, Dipper and Pacifica chase a Face-Stealer demon (who has stolen Mabel’s face) into the town’s Paranormal Black Market. Vendors include the Haggling Hag who sells Hand-Me-Down Hands and Bootlegged Legs, an imp who sells Nightmare Fuel (normal and premium), a wizard who sells stolen memories (“Unforgettable Deals!” says the sign on his stand), and Cryptid Currency. (Truly the whole place is a Hurricane of Puns.) Humans are not allowed here, but the guard at the entrance isn’t very smart and easily falls for Pacifica’s claim of being an elf bandit intending to sell Dipper on the slave auction. Dipper doesn’t exactly like that, but at least it gets them inside.

Film

Despicable Me has the Bank Of Evil (formerly Lehman Brothers).
Men in Black. Jack Jeebs provided exotic weaponry to alien criminals, such as the "reverberating carbonizer with mutate capacity" he sold to an unlicensed Cephalopoid assassin.
Megamind subverts this: he builds all his gadgets himself and he gets all his decorative stuff ("computers" that consist of nothing but flashing lights) from a small outlet in Romania.
In the second Hellboy film there is the troll market.
In the Cold Opening of Tomorrow Never Dies, James Bond infiltrates one of these. Cue Stuff Blowing Up and an escape in a fighter jet.
The entire country of Malaria in Igor, though it's less "buy our evil stuff" and more "pay us to not sell it".
Watto's junk shop in The Phantom Menace, although he'll sell to pretty much anyone who ponies up the dough.

Literature

Knockturn Alley in Harry Potter (Evil Counterpart to Diagon Alley). The most notorious shop there was Borgin and Burke's, a place where Voldemort himself worked when he still called himself Tom Riddle.

Live-Action TV

The underworld black magic market seen in one episode of Charmed.
An episode of The Unusuals featured a store that sold murder equipment.
The greedy alien arms dealer Broodwing from Power Rangers SPD, the Evil Genius behind the rare Orangehead Krybots and the evil zords used by Emperor Gruumm. Nominally, Broodwing worked for Gruumm, but was ultimately a mercenary who'd build weapons for anyone. His wares were usually very expensive, but the tyrannical Gruumm would often demand his work for free. Possibly why the Rangers were so easily able to defeat them, as Broodwing didn't seem like the type who'd give his best merchandise to deadbeats.
The Lead-Lined Shop is a place located in the bad part of Metropolis, detailed in a 1988 Mockumentary done to celebrate Superman's 50th anniversary. All of its merchandise seems designed with fighting Superman in mind, including Kryptonite of all varieties. (Continuity for the Silver Age still in effect.) Despite this, the owner claims to be a law-abiding merchant, indicating a disclaimer on the wall that reads, "It is a crime to utilize the items in this shop for the purpose of Evil".

Tabletop Games

The Champions supplement Gadgets! mentioned two organizations that sold weapons and other equipment to super villains: the West German KRONOS and Japanese ISE (International Scientific Elite).
Shadowrun. Fixers sell illegal equipment (including weapons and ammunition) to shadowrunners.
Planescape
- You can find literally anything for sale in Sigil, with places like this most common in the Lower Ward and the Hive.
- Dragon Annual #2 mentions the Consortium, a market on the Grey Waste the size of a large city ("without a doubt, the commerce center of the Lower Planes") run by the oldest covey of night hags in existence. They specialize in larvae (damned souls that fiends use in the creation of young fiends) but also sell larvae products, such as a perfume for temptress fiends called "Evil #7". They also have markets that sell weapons, slaves, and every type of contraband imaginable. The article even mentions a coffee shop in the place that sells Abyssal Brew.

Video Games

The Octopus in GoldenEye: Rogue Agent
Arguably, these exist in Vampire: The Masquerade – Bloodlines for the Player Character, though some may consider them to be anti-hero mart. These black-market dealers include- in order of severity: a pawnshop owner selling knives and 38. calibre pistols without a license; a bored clerk at a 7-11 offloading firearms to supplement meagre pay; a Chinese ex-military herbalist with several "remedies" that can only be bought with cash; a black-market dealer with more than a few ties to organised crime, working from the back of his truck; finally, there's Mercurio, a Ghoul arms dealer working for Prince Lacroix, capable of finding just about anything for anyone. A borderline case may be found in the form of Pisha the Nagrajara, a flesh-eating immortal lurking in the basement of a condemned hospital, who'll happily hand over some very useful items- provided you can find the occult items she's been searching for.
The villain-side "skin" for the City of Heroes auction house feature -- the Black Market -- gives the appearance of an Evil Mart. Subverted in that both hero- and villain-side share the same pool of merchandise, and there's nothing particularly villainous about any of it.

Web Comics

The webcomic Evil Inc. is all about one of these.

Web Original

For a short time in the early 2000s, there existed a parody website of Home Depot called Home Despot, which pretended to be the online version of Evil Mart. It provided our page image.
Uncyclopedia has 9-Eleven and Jihad★Mart for all your martyrdom and freedom-fighting needs!

Western Animation

Supervillain Supermarket and Deli in Codename: Kids Next Door; While a villain-exclusive place, the inventory seems typical of most supermarkets and even has discount cards and coupons. Numbuh Three seems to think the cookies are overpriced.
HenchCo in Kim Possible. Dr. Drakken goes there to browse equipment and minions, then considers picking up milk while he's there.
Harley Quinn (2019 version) goes a little overboard with this. In the third episode, Harley visits Underworld Talent Inc, a temp agency for villains and henchmen. (Harley is not welcome.) She then attends a seminar hosted by Maxie Zeus on super-villain strategy. Of course, Maxie is not the most reliable pitchman here; Poison Ivy claims he's stoned, and Harley doesn't get much luck there either.
In Trick or Treat Scooby-Doo, the Gang figures the best way to deal with all the criminals who pull the Scooby-Doo Hoax routine is to find out where they're getting their costumes from, and quickly discover that the fashion designer and crime boss Coco Diablo is indeed the one who designed the costumes for most of the crooks they've encountered in their entire careers. She was savvy enough, it seems, to build a second 10,000 Volt Ghost costume in case of trouble, using it against the true Big Bad of the special.
in the DC Super Hero Girls episode "Powerless", Toyman uses gold kryptonite on Supergirl which he bought online at a place called Very Deadly Space Rocks & More. When he realizes it failed to kill her, he makes a note to give them a one-star customer rating.

Real Life

In Real Life, there are black markets where you can get things you're not supposed to be legally getting.