Did you just break the slider?
Jeep Zipper Sliders
If you are looking for a whole new sew-in zipper, you can find these on ebay, Amazon, etc.
On my 05 LJ, I needed the whole sew-in zipper replaced. I took it to a local canvas shop. They had a difficult time getting it to fit right, but they eventually got it. Cost ~$70 : $20 for the zipper, $50 for labor.