I made a level_up_learnsets.h file where all of the pokemon given away in the frontier have greatly expanded movesets. Every pokemon can relearn all of the moves they can possibly have in all gens, excluding moves introduced in Gen 8 (except Mew whose moveset was trimmed to 255 moves). It should be as accurate as Pokemon Showdown because that is where I got the data. This solves the problem of egg moves being unavailable and simplifies the process of changing up your movesets, but kinda makes TMs and tutors pointless.
https://raw.githubusercontent.com/Artdog/test/main/level_up_learnsets.h
This also requires that MAX_LEVEL_UP_MOVES in include/constants/pokemon.h be set to 255. Changing this value doesn't seem to cause any problems.
Holy crap! How long did this take you? There's like 300 Pokemon in the hack! I'm so impressed. Between this solution and eventually (read: never) implementing new TMs, I'll take this in a heartbeat. In the next update, I can just add this and remove the move tutor house and TMs from the frontier shop. Again, thank you so much. This is very cool.