Some people replace zipper pulls with key rings (usually the people who resort to paper clips are CJ owners - but they fix everything with duct tape, a hammer and bailing wire. Nice to see some Mcguyvering on a TJ!)
A boat canvas shop is a great place and a very good suggestion, especially if the zipper is worse off than just a broken pull.
We dont' sell replacement zippers, but can point you in the direction of a company who does. Call our customer support team and ask for the BD Company phone number. I don't have it here at home.