I know sites like guitarbackingtrack.com have a lot of decent stuff on, but most of the time the stuff I'm looking seems to be really difficult to get hold of by Googling and checking these places.

Which sites do you guys use to find difficult to get hold of pieces?

Also as a side note if anyone knows where I can find/buy the backing for Come on Baby by Joe Satriani then you are a legend
You do know that UG has started offering backing tracks with their UG+ feature? But when it comes to rarer songs, I guess that's just the way it works, the sites have the backing tracks that earns them the most money and I guess they don't want to waste time and resources by recording backing tracks for songs that only a few people look up. Maybe you're just out of luck, although I'd say Joe Satriani is pretty damn popular.