It's best to go to Animal Planets petfinder website. All shelters and places have their dogs on their, and you can do a search for Chihuahuas on there. It's agood resource for finding local shelters too.
You should be able to find a Chihuahua rescue and adoption center in your area. Check the telephone book, newspaper and of course the internet. This is also a good way to find a Chihuahua breeder.