OK firstly...

PLEASE DONT BUY YOUR NEW PUP FROM A PETSHOP!

now, onto breeders, contact the chihuahua breed clubs, they will have the details of breeders in your area, not all will have pups at the moment so you may have to wait for the pup, but that would also mean you have the chance to get to know the breeder and the parent dogs before bringing your new family member home!

I am very jealous, would love a chihuahua but until i have saved enough to cover the huge purchase price i cant make that a reality!

hope it helps