Salvage yard or ebay. Ebay will cost more, but then you don't have wasted time tracking one down. If all you need is just the sicssors jack, you should be able to find one of those real easy at a salvage place with newer-ish vehicles. But if you need all the other parts, .....a lot of times you go to a yard and the handle is missing in this truck, and other parts are missing in the next truck. Can't find a lug wrench in any of them. Then it gets to be a waste of a morning. Also it's very likely with Chrysler, jacks/handles, etc could be very similar if not the same betseen different makes (Jeep, Durango, etc, even some Ford/GM jack parts are similar to Chrysler in 'some' cases) ..and years. I'm not sure what fits what anymore, but a little digging and you'll probably find out. If you go to a salvage yard, it would be good to know that.
Make a note of what other parts besides the jack are missing: Hold down fasteners, any brackets or pouches, handle crank, tire iron ...adapters to unscrew your spare. Best if you can get them in one package. If all you need is the actual jack, it won't be too bad. I ran into the same thing on a vehicle I bought a bit ago. I bought a whole kit on ebay from someone parting out a truck. Good luck