I got my two labs from Mississippi Mud Kennels of La Crescent, MN. granted they are American bred dogs, but his asking price for his puppies is reasonable. The two litters he had out of his females this year have been all sold but there is a litter that is currently for sale in La Crosse, Wi that his Male was the stud dog for the breeding. I believe there is 2 Black males and 2 Yellow Males, and 1 Yellow Female left in this litter.
https://www.huntinglabpedigree.com/puppy.asp?id=53320
there is also a lot of other litters listed on huntinglabpedigree.com beside this litter, you can search by state. American bred dogs are going for $1000 to $3500 per puppy now days. the few British Breedings I have seen have been $3000 plus per puppy. personally, if I spend that much, I will buy a pup out of an American nation field champion for that price instead of a British dog. To me the British labs are more like the American show labs.
Another option is that if you are willing to wait until next month there is some lab breeders that will have British pups at game fair in Ramsey, MN that will be for sale.
one other place to check is the AKC website. they have like this marketplace section on their website that you can do search for specific breeds and breeders by state.