I tried petfinder.org, and only found a couple chinchillas in Britsih Columbia, Canada, but I would recommend doing two things:

1. Learning everything you can about chinchillas - get books from the library, read stories on the Internet, etc. so that when the day comes, you will be amply prepared for your chinchilla. This will also help show your parents how responsible you can be, and that you are serious about your interest. And it'll be fun to learn more about chinny-chin-chinchillas!

2. Sending polite letters to every animal shelter and veterinarian telling them of your interest, so that if they know of a cchinchilla in need of a good home, they will have your letter on hand, and think of you!

Good luck!