Pretty easy to solve actually...
Part numbers for a 93 rear door latch - 5502 6382 and 5502 6383 (these will also work on 94-96 and possibly earlier than 93 as well.) Pick em up on any mopar parts reseller site. I'm fairly certain you can get them for 35 bucks or so on discountjeepparts.com as well, that's where I got my front right door latch when mine did the same thing.
You can also pull them at the junkyard (you'll need a torx set and some patience) for like ten each, expect to be dunking them in a parts cleaner or degreaser bucket and scrubbing the heck out of them, then regreasing with white lithium spray grease.
EDIT: handle it now (however you do - you can also pull and clean/regrease your existing ones if they aren't rusted heavily like mine were) before they freeze up entirely and you can't open that door. That's how I bought my XJ, I had to tear the crap out of the right front door trim on the inside to get it apart with the door closed so I could hit the force-unlock lever inside.