Just to close out this thread. My local Ace hardware stores are great, and very willing to order me a 50' roll...not what I needed, so I ordered directly from a West Coast Manufacturer.
www.rubbercal.com , a small order was no problem for them. A small word of caution is to make sure you orient the horizontal ribs to be horizontal with the opening in the door. I'm not sure how a rubber mat manufacturer can create a roll of rubber mat and not have the ribs be parallel with the the length of the mat, but they were able to do that... Product sure seams the same to me as my 50 year old sample, just a lot more flexible

. Blue painter's masking tape doesn't stick to it, so I'll probably experiment with some different slow acting glues to figure out exactly what will work. I will need to do some re-positioning of the mat once I get it laid down in place in the door. I had some small bridges welded in place between the inner and outer door pan right where the inner door panel cracks just above the top of the cardboard door panel. I saw several sets of nicely painted doors at the British Field Meet and they were cracking in this area of flex. The bridge is a piece of horizontally located sheet steel, so I just slit the rubber mat along a rib and slide it over the bridge. These little bridges really help tie the inner door and outer door together and are not very noticable. Now I just need to figure out how to glue it in place without making a huge mess on my freshly painted doors or on the occupant facing side of the mat itself. Maybe my kid's small hands will be helpful...
-Ken