The rubber is a Quarter Window Seal and they can be found at a number of places. Here is one, for example:
http://www.justmopar.com/store.php?crn=217&rn=456&action=show_detailThe windows have to come out and the frames disassembled in order to replace the seal.
I have some pics of the window assemblies here (scroll down page):
http://70duster440.com/misc.htmlThe only plastic in these windows (1970) are the gaskets for the window latch (where the latch passes through a hole in the glass), and a felt covered piece where the glass pivots in and out of the frame. It's inside the vertical piece of the frame and no-one repops them. They're usually rotted and appear white.
If your windows are in really bad shape it might be easier to replace the assemblies with those from a donor vehicle.