Esci (now in Italeris's hands and possibly Revell De) made a Land Rover LWB
109 in 1/24 with a bunch of small arms in it.
I have one and it's not for sale. 8(
Ltaleri, CyberHobby and Hasegawa make Jeeps in 1/24, Hase made a Kubel and
I beleive Utaleri also may have made a military truck in same scale.
In 1/25 Tamiya and Academy made several tanks including Centurions,
Panthers, JagdPanthers, Tigers, T-34s and SU-100s, you could always bash
them a bit to make them more sci-fi. Tamiya had 1/25 metal figures of
Germna and US soldiers that aren't bad at all and they do come with plastic
small arms an MP-40, Mauser, Garand you could always copt some (for
personal use of course).
Somebody else, Nichimo comes to mind but I can't swear to it, made some
1/24 but they are hard to find and probably not cheap. They are also older
so may not be up to snuff. But if you are imporvising sci-fi...
Tasca makes a Pz II in 1/24 Emhay makes 2 version of a Bedford 5 ton and
MAC Models some older Czech truck.
Check HLJ.com or Great models for a list.
Wespe makes a US 2.5 ton cargo truck.
Couple of diecast M1A1s.
That oughta hold you!