Does anyone know of any chihuahua breeders preferably within the London area?
I am looking for a short-coated male about 10-12 weeks old.

Thanks

Have you tried the Chihuahua Club?  They should be able to help you find a breeder that can provide a healthy pup bred within their code of ethics.
This is a breed often exploited by commerical breeders who don't care too much about the health of what they produce so long as it is tiny and desirable so well worth waiting on the list of a reputable breeder.

I can give you the name and details of a reputable breeder and judge.  He is my mentor, and I have no hesitation in recommending him.  You would have to be prepared to travel out of London, but he has some quality pups at the present time.  PM me if you want.