I would look at demographics for areas with more custom rides/collectors/restos. Custom painting just any car, even imports, is not as popular as you may think here. I have worked at a many 'o shops, even a restoration shop, and the majority of work you will find is collision repair. It's an insurance paradise. The custom shop I worked at actually got more motorcycle custom paint work than cars did, and it wasn't cost effective, so they eventually sold the business (which was torn down and turned into a bank).
Florida would be a good start though. Due to weather, the southeast and the southwest are havens for custom and classic cars. Restoration is still pretty good business here and the collectors market is making a good comeback now.
Also, Florida is the capital for car auctions, so that would be a great place to start your research.
Gary Noonan
'01 S/C VX / '18 Forester XT