Quite simply Will, there are
NONE!
Nearest decent one is S & T in Yate, Bristol, 01454 313162. They advertise in the VMCC journal and I have only heard good things about them.
There is a firm in Ammanford called Novelearth, who
claim to do plating. After the balls they made of dechroming and powdercoating my Ironhead swing-arm, and charging stupid money for it, I would not touch them with a long disinfected bargepole.
My advice is to avoid them like the plague.