There's a P2P app from the same era as KaZaA, originally released the same year (2001), that's still in active use today: Soulseek. It's a great way to find obscure music, some of which isn't on streaming services and is extremely difficult to obtain otherwise.

Usenet is good for less popular stuff too. Torrents die once the last seed is gone, but some Usenet providers have over 10 years retention, and you always get full speeds over an encrypted connection with no uploading required.

Edit: Support artists where possible, but sometimes there's music that's impossible to find, and that's when these services come in handy.