Adoptions don't always come by quickly, you'll most likely have to do a bit of looking to locate one. It's sad because there ARE so many out there in need of a good home but it's not always easy to find them.
When they are usually "discarded" they are either left free outside, dropped on the doorsteps of pet store, vets, etc. or just pawned off to an unsuspecting friend where it usually meets it's end.
Most animal shelters encounter them on a regular basis so I would definitely contact those in your area. Some do not adopt iguanas out so you might have to "fight" a little for it. Explain to them that you want to save and rehabilitate one instead of buying one (which you could do very easily). Show them you're knowledgeable and will be able to care for it properly. I say this because I heard of a couple of people having to go through that with their local shelters but they got their ig in the end.
Also check with your local herp association. That's how I got my rescue iggy. I was there for a meeting and a member presented her as needing a good home. It was not the first time an ig was brought to a meeting for adoption.
So spread the word out everywhere

Shelters, associations, vets, pet stores, etc. I'm sure that it won't take long before you find one.
In the meantime you can get your enclosure ready and maybe even prepare yourself a garden of ig foods (collards, dandelions, etc.). I know it sounds tacky but it'll save you a bunch of money and you'll know you're offering your ig top quality nutrition.
Especially if you adopt an older ig, some can eat you out of house and home! My Paco is about 3ish, a bit over 3' long and eats like a horse! She eats at the very least 2 BIG bowls of greens and veggies, half the time she wants a third and that doesn't count in her treats!
Keep us posted
Pixie