I can't help with where. But, please, please make sure they know what they are doing. Bettle metal is very very thin, and a bit too much heat will totally screw up your whole car (waves!).
Doors shouldn't be blasted (IMO) with sand. Walnut/media blasting is usually safer.
Don't mean to scare you but, make sure they know what they are doing (ie, probably not a good idea to take it to guys that blast tanks etc).