Having just spent a couple of hours pouring over Dance Shopper, DanceVision, and Casa Musica's sites, with side trips to the iTunes store, I can tell you it's not easy.
I can say that I often stumble over good songs at the iTunes store. Often the tempo's not quite right. But there's plenty of software around to fix that if the change needed isn't too great.
Something I do about once a week is visit the iTunes store "front page" and I listen to clips for the new stuff they're peddling. Every so often I turn up a song worth buying.
I find that I'm liking less and less of what's on the newest releases from the "regulation" music companies. And there's a lot of recycling going on. Surely we can't have tapped all the wells of ballroom music on the planet!