I had a set of S Model wheels powder coated by Bradford Powder Coating in Chula Vista and was completely happy with their service and pricing. They do a ton of wheels and a lot of Tesla wheels.
I had the wheels off the car when I brought them in. If they are on the car they don't remove them and dismount the tires themselves, they have an arrangement with a tire shop a few miles down the street.
Bradford Powder Coating 1879 Nirvana Ave, Chula Vista, CA 91911, USA +1 619-421-7747