If you go on the Kennel Club website
http://www.the-kennel-club.org.uk/click on breed standards, Toy, Chihuahua Long Haired, you will find a list of breed clubs - they will be best placed to help you, but I would be very wary of anyone who just happens to have a litter available straight away, Chis are so rare that puppies seem to be booked in advance from good breeders. ;)