A place to start is the Kennel Club website, www.thekennelclub.org.uk and go to their 'buying a dog' then 'find a puppy' section.At present there is at least one breeder with a buff dog listed (others don't specify the colour). Click on the name of the breeder to show the sex of the pups.
Otherwise , contact the local breed club secretary (again to be found through the Kennel Club) .They may know of breeders with litters now or expected or have 'a puppy coordinator' whose list you could go on.
Wherever you go, expect to be quizzed about your circumstances , by any breeder !