Since that was, I believe, the first year, odds are that any part is going to be pricey unless the person is unaware of what it is. Since they were basically a fastback Coronet, you might see if you can adapt one of those. The best likelihood is to find a project/parts car on e-bay with a good taillight and buy it, take the parts you need and sell the rest. On a situation like that you would probably break even in the worst case.