I found a body shop through contacting a number of different (Mustang and non-Mustang) car clubs. The list of shops they could come up with for this kind of work was really short. The place that did mine does crash work in the front of the shop while the back half always has three resto projects going and they get worked on whenever the guys up front get slow....hence it takes 6 months+ for them to get an average project car done. The cars being worked on along with mine during the time my car was in "paint jail" included an Alfa, a '70 Chevelle, a '67 Camaro and a '66 Shelby Mustang race car. Yeah, mine may have been the most off-beat subject in the shop but it also got the most attention from people who saw it there according to the owner.
Widen your contacts with clubs and hobbyists and you should be able to find a shop, it just may not be located around the corner.