Is there a source of aftermarket sheet metal for ct9a? I cannot find anything.

I've seen fiberglass but never metal. Many-a-donor car though.

I know you can find oem quarter panels and other body panels that you can spot weld and seam seal on for repairs. If you are looking for straight sheet metal to do custom work or repairs on, aluminum and mild steel are by far the most commonly used for automotive projects. Not all sheet metals are created equal though.