Robi, try the Cat Shack on/near Datchet Water; they are the UK Nacra dealer; so can probably accommodate you. Or Datchet Watersports. Datchet is very close to Heathrow and has a good cat fleet, so making contact with the club itself may work for you as well.
http://www.cat-shack.co.ukhttp://www.dwsc.co.ukhttp://www.datchetwatersports.co.uk/ 
