You are probably better off posting this under general on the board, it will generate many more replies.

When you say he is refusing to send out his KC papers, is the dog:
A) A puppy which was advertised as KC registered with papers but none have been given? In which case you should contact trading standards. If the papers are late or you are being fobbed off, if you have the name of the Dam you can contact the KC and they will let you know whether the litter has been registered. However, they will not send them to anyone other than the breeder. New puppy owners can not get the papers, only the registered breeder.
B) Or is this an adult dog or older pup bought from someone after the breeder? Wherein for whatever reason the previous owner is not wishing to forward the papers, again only this owner can sign the transfer of ownership forms to pass onto a new owner, you can not get them from the KC yourself.
In both cases there is no way you can get hold of the KC papers without the previous owner/breeder transfering them to you.
All you can do is take the dog back as it has come without papers or if you were promised them contact trading standards.
Some breeders and rescues refuse to give papers due to not wishing the pups/dogs to be bred from rather than endorsing the KC papers, this may also be a reason but you should have been told there would be no papers at the time of sale.