This photo shows a hard-to-access section of rust damage—unless you remove the fender!
I searched for the replacement panels for the affected area but couldn't come up with anything, so Brian Nordby is going to fabricate what is necessary.
I suspect Chevy made very few, if any, replacements for these types of panels. If a car was damaged enough to require these panels to be replaced, it was a total loss.
I'm certain Chevy didn't think about crazy people repairing rust damage 34 years after the car was built!