It is not just the Sport coupe (bubbletop) that shares components.
Buick, Pontiac, Oldsmobile, Chevrolet have all been based off of the same platform for many years. The sheet metal may vary and these cars look very different, but look closely and you will see how very similar these cars really are. the roof line on all the full size cars are shared.
Look at the full size 61, 62, 63, 64 Chevrolets, Pontiacs, Buicks, Oldsmobiles,......Not just the bubbletop cars (61, 62) but the impala roofline. It just would not make financial sense for GM to have every division have exclusively specific parts for each make. Seats, glass, frames, (buick Pontiac olds, share rear axles, transmissions) many parts crossover. look at a 57 chevy hardtop and look at a 57 pontiac or oldsmobile.
The roof and glass are the same.
If you keep this in mind at the junk yard, you my find the part you are looking for but not on the chevrolet that has been been completly picked over, but on a buick, pontiac or oldsmobile of the same year and body style.
I could go on and on ........but you get the idea, don't you??