This is a little closer to what you might be looking for--a tent with laptops and maps.

Even this might be too fancy for mercenaries depending on what kind of unit size you're depicting (not so much the image, but the backstory size).

If you look at the movie Blackhawk Down, the soldiers on the ground didn't have anything more sophisticated than radios and paper maps. That was all special forces units. Mercenaries probably wouldn't be any better equipped than those soldiers. Mercenaries might have laptops in a jeep and satellite phones on them and you should be able to find freebies to serve that purpose. The above image would be the kind of Army command center managing around a hundred soldiers in over a dozen vehicles.

Try Google searches in their images section and this site to try to zero in on what you want.
http://www.militaryphotos.net/
There are going to be a lot of misses before you find something of interest, but that's how I found the images I posted--and it wasn't easy. There are a number of mercenary games out there that might help figure out what they'd carry.

My visual indexes of Poser content are at http://www.sharecg.com/pf/rgagnon