There are starmaps in the UCF sourcebook, the Arahnid Empire sourcebook and Army book, and the Skinnie Army book. The problem is that none of them covers all of the territory, just the bits and pieces. The maps are also not to detailed either. The Arachnid Empire lists the individual planets by name (no system name except for Klendathu's system...don't recall it off the top of my head). It seems like it would definitely be possible to piece a complete starmap together from all of these sources and give you some kind of idea what you are dealing with, but it would not be the most accurate.
Oh, and as for the Forth, they are located somewhere near the Skinnie, Arachnid and UCF borders. First contact with them was on Spartan IV, a world contested by all three races, and resulted in the Forth starship being damaged and crashing into the planet. This info is from Dantes Rift scenario in the scenario of the week section.
