First off, I have never found an 89 K1500 with a factory sun roof so I would first try to see if you could find a brand name and even a model or dimensions on the sun roof and see if they have a website where you can purchase a seal from them. If you can't get anywhere with that route, I would try to find a local shop that installs aftermarket sun roofs and see if they could sell you a seal or at least find out where someone could get one.