A good place to look for body parts are auto dismantlers, sure you may have to look for a while to find one that isn't completely useless or has no dents. Trust me though, for the price, it will be worth the work you put into looking for the right one.
Also, if you are looking for a new fender you can always check out black dragon automotive (http://www.blackdragonauto.com/). If you check their website you can ask for a free catalog and browse all the body parts that they have. As I said before they are all new. However, they are much more expensive then buying a used one, but, if you are serious about getting show quality results out of your restoration then it will be worth the extra money. I just simply recommend the auto dismantlers because you said you were on a budget.
happy building!