It might be easier to just make your own repair pieces if you don't care about it being exact. It would probably end up being easier than having someone cut out a non-rusty piece of their car and sell it to you so you can weld it into your car. It also might be difficult to find a non rusty car that someone is willing to sacrifice (unless it was wrecked, I suppose).
My 2¢. Take it or leave it
