Has Graydon ever discussed his process for finding obscure music?

I really enjoy listening to Graydon's playlists on Spotify and I've been wondering what his process for even finding this stuff is. I know he's talked about how he likes to deep dive into a great artist's lesser known works to find hidden gems, but has he ever talked about how he finds out about the music that practically no one has ever heard before? Would love to know and if any of you have any tips/tricks to find hidden gems (particularly of the 20th century) I'd appreciate them!