DI.fm has a lot of new / not mainstream artists. I've found a few artists on indie mixes of "inspired by" movie / game. On that note Overclocked.net is another way. Game music seems to have a few good ones. So indie game studios would have a lot of relatively unknown artists that don't get a lot of attention. Soundtracks are usually up on YT.

There's a radio station in the area that also has a strong indie upcomer musicians, but itxs really hit or miss because it's a grab bag of stuff which may or may not click and 80% of the time they play "traditional" stuff.

Find a station near some college town too. That's usually where a lot of artists get their start and college DJs are promoting indie stuff all the time. Websites and broadcasts.

Lot of the stuff is just out of the main stream way and you have to seek. But there's a rule of the universe that if you seek, what you seek will seek you back. So I hope whatever itch you need scratching finds you.