Just to be clear. Why do you need the whole Bonneville quarter? If you have a solid wheel opening a good metal man should be able to make a panel or at least what you need unless yours is complete scrap. I have used 4 door quarters and dog legs to make 2 door parts but it takes time and patience.
My current quarters are in really good shape, but they're aftermarket (20 + years old) and they aren't shaped right for a fender skirt.
I cannot find a body guy in the area that will touch them. A couple have suggested patch panels (or similar) that are shaped right and then they would cut out the wrong section and put in the proper section. Seems odd, but it's what I'm dealing with.