Try Steele Rubber Products. They may have the gasket material for you.
I'll second that,in fact I need to get a windshield rubber from Steele. I found out about cheap repops the hard way!
1950 Chevy Advance Design 3100 in Scotland In the Stovebolt Gallery More pix on Flickr. I've definately got this truck thing in my blood ... my DNA sequence has torque settings "Of all the small nations of this earth,perhaps only the ancient Greeks surpass the Scots in their contribution to mankind" Winston Churchill.