I would contact the breed clubs. They will havea puppy list coordinator who should know who has pups at the moment or pups planned.
The breed clubs tend to impose stricter rules over and above the kennel club with regards to how often breeding, how many litters the bitch can have etc so they are a great place to start. They should really be able to point you in the direction of good reputable breeders of healthy, kc registered puppies.
link to british chihuahua club Puppy coordinators: Mrs. C Shallcross 01793 878261,Mrs N Armstrong 01908 232607, Mrs D Lunney 01322 555324, Mrs T Barker 0208 529 1815
link to midland chihuahua club Sec. Mr D Smith. Tel No: 01902 831679
other clubs:
CHIHUAHUA CLUB OF SCOTLAND. Sec. Mr G Baxter Tel No 01383 724368
CHIHUAHUA CLUB OF WALES. Sec. Dr Curr. Tel No: 020 8743 4073
LONGCOAT CHIHUAHUA CLUB. Sec. Mrs Lee. Tel No: 01635 278510
NORTHERN COUNTIES CHIHUAHUA CLUB. Sec. Mrs C A Barlow. Tel No: 01524 752621
ULSTER CHIHUAHUA CLUB. Sec. Mrs W McDevitt 028 77765191
WEST COUNTRY CHIHUAHUA CLUB. Sec. Mrs M Greening. Tel No: 01249 783522
Have fun finding your pup!