My '80 Bonneville got bumped a few years ago. No problem fixing fenders and such, but the huge rear taillight assembly was shattered.
After they received the new part (junkyard from an internet search) the shop called me and said you better come in. It was intact, but completely faded and dull. After a week he was able to find a nos part, but the insurance company wouldn't spring for the cost.
Old car parts are hard to find, and don't even think about a Pontiac. Some Ponch dealers now sell Kias...LOL.
Hope you have better luck.