The search space is all tunes that have been played on Soundwave from all sources plus a large source with a huge catalog. Soundwave sources include Android Native, iTunes, Spotify, Deezer, Rdio, Pandora, Deezer and a few others. The authority source has a about 20 million tracks.
Bandcamp is not something we have support for right now, but it's been requested a number of times, and we like to listen to our users. Soundcloud support was a result of a very vocal group of users with the same perspective as you have.
Stay tuned!
