Through 1990, Jeep used Delco alternators with internal voltage regulators (Delco CS-130 for XJ/MJ, and I think 12SI for the YJ.) They swapped to Nippondenso across the board for 1991, with the regulator circuit in the PCM.
Any local shop should be able to upwind a Delco for you without too much trouble, and for not too much bux. If you can't find one by you, here's the shop I've been using for a number of years - www.kelleyswip.com/sjg.html
. There is an ID guide on the site that will help you determine whether you've got a CS-series or an SI-series (I'm not sure, since you don't mention model. I could guess that it's an XJ or MJ, but I don't like to guess...)