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.
Wish I could find these canvas places, everywhere I went to around me wanted $150-$350. There for my rear zipper is still broken. The rain stays out but I have been just duct taping it shut for the winter to keep cold and snow out.
Look for canvas shops in areas that have boating, and areas with a lot of trucking.
You may want to inquire at a marina, or a truck stop/truck repair shop.
Also consider checking at a saddler.
The key is a shop with a sewing machine that has a deep enough throat to be able to turn the top while on the machine.
Be sure to wax your zippers every once in a while! I have used an old candle, Chapstick and bees wax. Believe it or not, the Chapstick has worked pretty well!
__________________ But the wisdom that is from above is first pure, then peaceable, gentle, and easy to be intreated, full of mercy and good fruits, without partiality, and without hypocrisy. James 3:17 (KJV)
I broke a slider and was able to get a replacement from a local awning/boat cover shop. I replaced all the sliders on the side windows with double pulls so now my passengers can open them up a bit from the inside.