I've seen several sold on ebay, usually not very high of a price, in the same sort of condition you mentioned. Even though its not NOS since its painted, if you clean it up, take a picture of the GM sticker on the inside and some explanation, I think you'll still make out fine. I have a OEM Driver side, but sadly, while pushing the car into my garage when I moved here, the car hit the garage door, and put a dent in it. It wasnt in bad shape prior that. I found a replacement GM OEM RS fender for $50.00 on ebay, but the guy must not have known what even a used, but in excellent shape OEM fender would bring. I got the fender on a "buy it now" deal. Anyway, Im rambling, but I would still say, to both of yall, dont mess up a OEM RS fender, they are very short supply, even if they arent NOS.
Merry CHRISTmas.