I buy a lot of stuff from "Chevs of the 40's" they sell parts up to and including 1954. www.chevsofthe40s.com/ John
I haven't bought from them yet but there is an Alliance vendor that sells rubber from various manufacturers. I will be calling them soon. http://www.weatherstripspecial.com/
I don't know how close you are to Dayton, OH, but there is a place called Restoration world. They sell a lot of the same stuff everybody else does. I think the site is called chevroletrestorationworld.com. I bought all of my sheetmetal from them and they just released one piece front and rear bumpers for sale. Nice guys to deal with too. If all you need is a windshield seal, and you want a good one, buy one from Steele Rubber Products. They're the most expensive, but my glass guy says they're the only ones that fit right.