pretty much nothing I think you'll find.
Bulgaria has been a significant route for illegal drugs into Europe, they are very hard on it, maybe due to them being under pressure prior to their accession to the EU. You can probably get hold of some from some dody geezers , especially in resort, but taking stuff from people you don't know in a place you don't know isn't something I'd do.
theres plenty of white powder in borovets its really cheap all you have to do is stick your head into the snow and ya finger in ya hole and take a deep breath and its free