I highly recommend Popsky for that. (Dunno about spelling the username but that should bring up his yt channel at least) He specializes in choptune stuff and everything is dmca safe, and even does commissions.
There’s old music libraries that have tracks randomly posted on YouTube, pretty positive most of them are royalty free and made ages ago, just search “library music”
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https://x.com/RuneScape/status/1270839410469339137?lang=en
https://m.youtube.com/watch?v=YtF6jiLxc88
You could use My Funky Town by Toby Fox cuz it’s an unreleased song.
There’s one gramophone song from Paper Mario you could use.
The audio for steamboat willie
The half-life sound track but backwards and with a train horn noise every few seconds
Twinkle twinkle little star
https://youtube.com/playlist?list=PLUXl043M6v4NxohFiElWT4KUUOHc84PEk&si=Jj4kb-WzjkhOSKG5
try just looking up synthwave on youtube or something
Just grab a bunch of linkin park and shove them all through a vocoder lol