Try these guys...
Specialised Paintwork - Contact
They are near Porsche in Calcot. I had a car park door dent on the GT-R repaired by them. Very happy with their work.
Depending on the damage to the wheel you might want to consider http://www.myalloys.co.uk
in Basingstoke. They do full refurbishment of wheels. I had one of mine fixed a couple of years ago and they did a very good job of matching the colour. Incidentally, this is a multi-stage process. They stripped the wheel completely, repaired the scuff and then a three-stage paint process to get the desired result. First a black base coat, then a translucent dark-chrome 'effects' coat and then clear lacquer. My repaired wheel has a higher standard of finish than the other, original wheels.