No idea about breeder but farmer down road has daughters connie gelding (think about 8 yrs old, 15hh) for sale as she has totally outgrown him. Forward going, huge jump, hunted several seasons, never known him to have problem. PM me if you want to know more.
Whitley village stud is south warwickshire/ near Cirencester. She has lots of foals, 1, 2 and 3 year olds for sale. Good breeding and has full or part breds. Just bought my 3 year old connie x ish from her and she is fab they have a Facebook group and the owner is lovely if you want a chat.
A few years ago PRL performance horses (in monmouthshire I think) used to import very nice connies from Ireland. One of mine came from there and he was a fab little pony. They're dealers as opposed to breeders but have some good stock (or at least they did a few years ago!). What exactly do you want it for, as I know of a couple for sale in Wales if that's any help?