Some dealers still have some old stuff, you just have to find it is all. By some I mean, more than 1, but not very many. There's also a few dealers who seemed to like to buy up everyone elses NOS parts, Friesen Chevrolet comes to mind, among a few others.
If you have the part number for said panels, you can plug it into partsvoice.com and see if any dealer has it lying around, call them up and have them ship it. I've bought a few parts this way.