Hi Dan,
I would recommend Ebay. They have originals occationally, including one currently I believe. It doesn't use rubber. It does have a cog with very widely spaced teeth. The stainless "arm" that pushes the window out, curved so it will hold it's shape, but somewhat flexible also, has widely spaced wholes that accept the teeth. It is pretty easy to install excepting rusty screws. Just get a whole unit, including the pusher "arm". Then just bolt under the dash, and attach the arm to the windshield with two screws...easy.
Make sure any auction advertises good teeth and drive units. I'm sure they can be found new from the truck guys, I think, but some good originals still out there from my Ebay hours
