Any tyre shop will be able to take the tyres off the rims no problems, but I doubt they'll be happy to have your car sitting around on stands whilst you get them powder-coated.
Your best bet would be to place the car on stands at home, then take the tyres/rims to the tyre place, have them removed the tyres, take the rims to get coated, then return to the tyre shop to have the tyres put back on, and put the rims back on your car.