Here are some of tested and suggested mods for Jagged Alliance 2: Unfinished Business. If you have more that you'd like to share here is the exact place.
Note. It is better to test each mod with gog installer first before you add new one to this topic.
1. SOG 69 Mod
1969 Vietnam. SOG hires a cilivilian team of mercenaries lead by YOU to find and destroy COSVN using any means necessary. New weapons, items, mercs, but same deadly combat:
http://www.vietnamsog69.50megs.com/.

We will check it and answer that question asap.

1.13 is a mod designed for pure JA2. One of its feature is adding weapons and NPCs from JA2.5 (UB) to JA2. We are sorry but for now there is no JA2UB 1.13 mod. But some fans created 1.13 version for Wildfire so maybe, just maybe, somebody will create 1.13 for UB :)