Hi and welcome!
We do have a very active member who lives in SD, but her child has multiple things going on, so I believe they go to the Mayo Clinic.
Just because there's no one on our list doesn't mean that there's no one there that can treat a PWS. Have a look:
You'll just have to call around and get references when you get there. If you are moving with a corporation, this might even be easier. Get in touch with the insurance company.
When are you moving?