ZF builds high end parts. Like frogslinger said they are used in BMW, Porsche, etc... They also build power steering racks, pumps, transmissions... I'm assuming they went to ZF because of Fiat. Definately not a bad thing except for those that want to change to lockers or change gears. If you open it up and get a part number off the diff I bet it can be cross referenced to another vehicle and you should be able to find what you're looking for. Might be the same diff used in one of the older land rovers or maybe the MB G-wagon. Unfortunately anything for ZF is usally expensive so you may want to brace yourself before checking the prices. Some of the gears in the ZF transaxle in my Porsche cost 600-800 each and the diff is $1600 or so. I'm sure there is some Porsche tax added but the parts aren't as cheap as for a "normal" truck axle.

I bet ZF is the supplier for the new 6 speed transmission being put into some of the other Chrysler vehicles.