I am working on one of my Master Lists, but the /r/darkjazz subreddit was good. Now, it is mostly dead but for spam from randos who aren't within miles of the sound trying to flog their own efforts. Black Chamber, Free Nelson Mandoomjazz, you might try those for giggles.

I had expected that some of Badalamenti's stuff would have opened up since his death, like his score for Witch Hunt, but no luck. His stuff was sort of a wellspring, among others, which intermingled into that little creek we called darkjazz, for a while.

I originally got into it as a primary component of a long set of mixes for a particular mood, namely that I would have instrumentals (primarily darkjazz) buffering slow tempo "torchy" kinds of songs (Mel Torme, Julie London, Nat King Cole, Billie Holiday) and the "once every ninety minutes" track which was a little newer. The idea being that the darkjazz doesn't call too much attention to itself and keeps the mood going.