If you have your heart set on a chihuahua,
you might want to check out the internet for
a chihuahua rescues.
(the only reason why adoptions are strict is they
want to make sure the dog goes to a good home.)
If you have no luck with a rescue, than
how about a reputable breeder.
You can usually find a list of breeders at
the AKC web site.
Purchasing a pet quality puppy from a reputable breeder is
cheaper than buying a pup from a pet shop.