Ugh!!! That sucks. Florida rust.
My Challenger has the same issue. I had to source a complete roof for it, at the time only one company was making that section and was only making it as part of the whole door opening structure.
AMD did just release some of those sections for the E-body Barracuda’s. Obviously they’d be a little different but if you can’t find a donor it might be better than starting from scratch.