Googling gives me this (I have no idea what they are like).
But from watching lots of Wheeler Dealers, and having a good knowledge of tinkering, I'm sure you could find what you need. Have you taken the A/C unit out to see if it can produce pressure?
Over 60,000 Brand New Auto Air Con Parts available. All types of car air conditioning condenser, aircon compressor, air con pump, air con radiator. Any car, truck or agricultural vehicle. Free delivery and 3 year warranty.
www.autoairconparts.co.uk
EDIT they have two compressors for £484