Likewise, not sure of a UK supplier....you could try asking member Superlight3:
http://www.ducatisportingclub.com/pr...o=newpm&u=7523 These guys are VERY good however:
http://www.kaemna.de/cms_en/katalog....el&artikel=234 
I'd recommend going for 4-piston calipers if you are upgrading, well worth it.
Cheers - Frank