I got the universal weatherstrip flocked rubber from ebay for my sliding windows, I it was 1/2"w x 1/2" h with the glass opening 3/16-7/32 inch. Worked perfectly for the sliders.
A local glass company had the slider seal material in stock. If your talking about the base seal for the upper windshield, I have no idea where you'd find a replacement. I went with a 'wet' seal and used Sikaflex.