I`ve looked for those clips for years and never found an exact replacement. Most people find one that fits the trim and then bend the clip to set correctly on the door edge. If you do find any, please let us know. Good luck!
Look on this page . There are a couple of different sized clips for early Plymouths. I cannot remember which one I used, but I got them to work just fine. Darn old brain, but they do list the dimensions for the clips if you have one of your old ones to use as a template.