These are the tropes that are one step beyond Dead Horse Tropes; not only are they not used straight, they're not used at all. You won't find this in any current series; they have disappeared from the writer's toolbox.
Note that these aren't actually forgotten, Future Imperfect-style, otherwise would we even be talking about them here? Academics will know all about them, and a few minutes with a web search engine will turn up plenty, if you know what to look for. They may, on very, very rare occasions, show up in a modern series, but generally only those that are emulating a series that did have these.
The best place to find Forgotten Tropes is in "classic" works; there you will see them, frozen like insects in amber. For example, in Alice in Wonderland, Carroll's poem about the "little crocodile" parodies Isaac Watts's saccharine original about the "little busy bee" -- an example of a whole class of Victorian poems that children were taught in order to instill virtue. (See Weird Al Effect.)