boat window rubber gasket seal is manufactured by high quality epdm. It is mounted around the glass window with a large range of applications including cars, trucks, trailers, caravans, high-duty equipment, boat, etc.
abcrubber.com
You might try a windshield glass shop.
If you have gaps that leak, you can get away with using black RTV or silicon caulk
It would help if you gave more info on what seals you are referring to.