The Kennel Club has a list of Breed Rescues. A popular breed like Cockers probably has regional ones. The KC phone no is 0870 606 6750, or try the Web site, though I find they take a while to reply using that route, easier to phone!
The National Co-ordinators for Cocker Rescue are Mr & Mrs Pain (tel no 0121 453 3215)who can put you in touch with a regional representative.If you are in Scotland, there is a different number so let us know where you are! If you are looking for a young bitch, v few of these come onto Rescue & you may have better luck contacting individual breeders to see if they have anything suitable.