Weatherstrip for a 1987 Cadillac Brougham

The weatherstrip on my Brougham was going bad (missing a section about 4 inches by 2 inches in the middle of the drivers side door) so I decided to replace it. This is the first time I've ever dealt with something like this. Well the stuff I got to replace it was not meant for replacement. I've checked both Autozone and Checker, both of whom say they can't get in the custom weatherstrip for it. I went to JC Whitney and they said they don't carry anything that will work for my car. I've checked a few other places online and can't seem to find anything that looks right. Where should I be going to get this stuff?