I've been using newsgroups for video downloads for quite a while. The Arr suite is great for this. On the same note, I tend to find a good deal of music with Lidarr and my news server, but not everything. Notably, classic rock and older albums are more obscure. I supplement this with SoulSeek, but that's got its own issues.

What other options might be available that I'm probably overlooking?

Edit: To clarify - I'm trying to find other sources or options for finding the music that's more difficult to get from the sources I mentioned.