That edging is standard rubber/vinyl edge trim, with a metal clip molded into it. It is sold at many marine/camping stores. Be sure to get the type with an aluminum clipping in it, not steel!
The BIG advantage of buying from Rudy at D&R though, is that you might not have to try to figure out how to measure how long of a piece you need to go around the whole deck edge! (edge of CB cap was also covered as well). Then again....... the WIDGEON that Rudy was building/selling was a newer version that did not have that edging material, the whole cockpit was molded as part of the deck, unlike your (and the 1969 model that I used to have!) boat's open design (narrow deck around the gunwales, molded-in seat across the boat, and flotation tanks in bow and stern). I'd stil lgive Rudy a call, last that I knew he had an older WIDGEON in his yard that would have had that trim originally, alas long gone now! (boat had actually been disassembled by someone restoring her).
I have added 3 pics, 1st is a 1987 model, but shows the molded interior that the boats Rudy built had, 2nd and 3rd show earlier boats that would have had the edge trim. Note that the one with the blue deck does have the trim in place!