If anyone will sell you a puppy in time for christmas I wouldn't be buying from them!!!!
Any reputable breeder would not let their pups go to new homes at this time of the year.
If you contact any of the Breed Clubs, they may be able to put you in touch with a breeder who will have puppies available in the New Year, but usually you will have to wait for a Border Terrier pup which has been bred for the right reasons.