From what I've heard on the subject.... it is very specialized work and very few people will even attempt it. There is one fellow here in PDX that does some, but no guarentees on it. They can crack when being reshaped, some are not doable, and the service isn't cheap.
This is all what I've heard since I'd just avoid a bent rim in the first place. If I were interested in restoring one I'd have to verify that it could be done before getting it. You know how adds are.... LOL oh it's just got a little scratch and then half the car is bashed in...
my 2 cents
AF