You mention the Stalkers sprues; most minis on there are very specific and easily recognisable.
I used several of them on my BSC entry last year, and I found that they can be easily converted using 1/72 militairy miniatures. For instance I had some Airfix NATO groundcrew and some Tamiya US groundcrew, as well as a multitude of others to play around with.
Most of those had been lying in the bits box for decades, but I finally have a use for them now.
Check around if anyone has any 20mm / 1/72 soldier types lying around, nab 'em and go to town. Not all Stalkers are suitable (the exo-skeleton ones for instance), but with a bit of faffing around, you can easily get another batch of 12 uniques out of the existing set...