For GUKPT, why our very own BlueSq of course
For WSOP, EverestPoker are the Main Sponsor I believe. I think your best chance of finding Sats would be on Stars, FT and Everest. I believe a few APATers have been successful in securing seats through Virgin and Ladbrokes in recent years.
And I think I"m correct in saying Stars are the front-runner for most things EPT.