There are a few ways to strip paint or PC. Most 'effective' being using a chemical stripper (Youtube style lol) however this may seriously compromise the integrity of the wheel/material. Dbl-check with your favorite chemist (not the wheel-shop dude) before dipping your AL wheels in anything
The proper way would be to gently sand blast them to remove the top layer and then using a vibrating tumbler to finish/polish the material. Look for Machine Shops in your area, they normally also specialize in metal surface finishing and should be able to point you in the right direction - if not already geared up to do them for you.
Hope this helps