Yeah, I’ll echo the soulseek suggestion. It’s trivial to find anything but the most obscure stuff, and even that’s possible. I have something like 4tb of total shared files, of which about 2tb is music, almost all in flac format, with acceptable tagging standards. And I’m a lightweight on soulseek.
Throw in musicbrainz to flesh out the tags, and you’re good to go.
Just be sure to share some of your stuff back, and you’re set. There are people that won’t let you download from them unless you’re sharing, so it matters.