My pal Buddy has a '76 Eldorado convertible that needs the white interior door panels. He described it as the center section, with the window controls.
Where do he get some of those?
Alrighty there... You or he have two choices. You may buy the reproduction (hard plastic) ones (door arm rests) or simply recover the existing ones with high quality leather or vinyl and a French seam at the upper bend. I have done both on different cars and I suggest letting a decent upholstery shop cover the original arm rests with a very high quality, smooth vinyl with said seam. The hard plastic looks cheapish. Done correctly the covered original will look better and more expensive than new.