I've used these people:
Professionally mixed car touch up paints using the highest quality paints so your stone chip repair lasts for years to come. Custom mixed car touch up paint with quick delivery from £7.99.
www.cartouchuppaints.co.uk
The paint is top quality with high solids, and excellent spray nozzles.
I bought both silver and blue for my Pinin.
Only issue, which wasn't their fault, is that the blue paint match was perfect matching the door shuts, but you can't allow for 20 years of paint fade...