I would suggest you contact Gites de France - they probably have a website, but I don't know it by name. Remember that the French spell things differently .... Normandie for Normandy and Bretagne for Brittany. You could also contact the tourist boards in the towns or areas you might like to visit as they also keep accommodation lists, and in this part of France, they should be able to handle queries in English and give a reply in some form of English that you will understand!

As you have probably discovered there are hundreds (if not thousands) of gites with pools in Brittany - the key is finding one close to the coast (and a bit of coast with decent beaches) In my experience owners will advertise the closeness of beaches as "good selection of beaches within 30 mins" and what this means is if you know the roads and are driving at breakneck speeds out of high season you can just about make a couple of beaches within 30mins!!

Thanks everyone for all your help and information.