I dealt with this company for my entire 6BT Dakota project from everything from 4" s.s. to 2" alum and everything in between. Great people to deal with.
We use powertherm co inc. Out of houston, tx 713-682-6777 for just basic bends any size. And then we auto-jet muffler corp out of des moines, iowa for some trick 180* 5" bends makes twins easy and you dont have to butt 2 90s together and there # is 1800-247-5391.