Why do people call them 'british' bulldogs? They are Bulldogs, pure and simple.
Please do not buy one without a proper pedigree, you have no guarantee that it is even the correct breed. Go to a responsible breeder, who will have registered the puppies with the Kennnel Club, and make sure they have had any health checks done. Look up breeders on www.champdogs.co.uk go to guided search, then utility group, then bulldogs, then breeders. This will give you details and you can contact them to ask about their dogs.
You are going to have to spend a lot of money, so make sure you get what you pay for!