That goes for all other pets too. Cats, Ginuea Pigs, Turtles, Hamsters, Gerbils, Ferrets, Birds, Fish, Snakes, Horses, etc. I was amazed at how many different types of pets need to be rescued.
Try PetFinder for starters.
You can try PetSmart too, and I'm sure there are more if you don't find what you want in these two places.