TheForvalaka

I’m gonna second Soulseek. It is pretty old, but so many of the people who use it are collectors who organize their collections well, and I’ve found some pretty obscure stuff on there as well.

I haven’t tried it myself, but I want to try Soularr, which apparently lets Lidarr use Soulseek as a source.

Another +1 for CWA. I tried several solutions and it was the right one for me.

If you reach the point of looking for a different solution, check out Calibre Automated. I tried several different things and this was the best one for me.