Here's a good place to start: http://www.imperialclub.com/index.htm Especially here: http://www.imperialclub.com/Part/index.htm This might too: http://www.moparts.com/index.html And this guy seems to have NOS weatherstripping: http://www.collectorsautosupply.com/query.asp?section=WSTRIP&year=54&make=Chrysler His main parts page: http://www.collectorsautosupply.com/parts-lists.htm
You may want to check with Steele Rubber and Soft Seal. They carry a line of specialty extrusions for universal use. We have used these in the past when an exact part is not available. Just about any part they carry can be bought in a bulk roll or length. You just need to ask.