For old car parts, ones that need restored, Hemmings Motor News is the only way to go.
Try a news stand to get a hard copy.
Follow the link and maybe you will find what you need.
I looked around but came up empty. Many cars back then were very similar, perhaps repair panels for a different model will work. I'd post here http://www.teambuick.com/forums/archive/index.php/f-74.html and ask about that or if someone there knows where to obtain these panels. Hope this helps, good luck.