Where can i find truffles in bulgaria?

my grandfather and his friend want to go truffle hunting and there wondering where can they find truffles in bulgaria??? any towns or regions or forrests would be very helpful, if you know any around Burgas its preferable, but if you dont any other ones would be helpful, also can someone give me truffle hunting techniques, and do the dogs have to be specifcally trained and also do pigs have to be specifically trained, thx :)