In my opinion you have to call a junk yard to find the parts you need. There are a couple of parts places that may have them but they will be hard to find. Try Old Car Parts at (503) 771-9416, they have had a bunch of original parts I needed for my car.
If your interior is the same as the sedan, the armrest sits on a very dense fiber board that is formed to the shape of the interior. The fiber panel has the rubber armrest that is glued to the upper part of the fiber form. If all you need is the rubber armrest part, you could cut that from a dense foam.
The fiber panel also has a piece of wood in the shape of an elongated pyramid that is nailed to the rearward part of the panel and screwed to the body at the apex. There are several pieces of hard cardboard that are used to form edges for the interior cloth that covers the fiber form and arm rest. There is a separate upper fabric panel between the top of the arm rest and the underside of the window. There was a tar covered cloth that protected the fiber form and interior cloth from any leaks around the window. The fiber form is held in place by metal tabs at the bottom of the wall. This is a short
video I took when I pulled mine out, it may help explain how this fits together.
Brian
