thats gonna be a tough find here, this site is geared more to the 97 and up grand prix's.
there are a number of parts places here in the US tho that re stamp parts, not 100% sure on your quarter panel tho. used are getting harder and harder to find as well as the years pass.
not sure if year one is making GP body parts or not, but they are worth a shot.
i took a look over at year one.com. grand prix and GTO, same thing back in the day right? they sell quarter panels here at year one. https://www.yearone.com/Catalog/1964...-panels-.-full
good luck rebuilding your car. the old ones were the cool ones for sure.
