Ian (my brother for everyone who isn't Moz) briefly suggested building a clay model mask and making a 95% accurate mould. We could most likely do the clay part, but the moulding... we don't have experience with.
At first we were planning only Civil Protection (using CG guys in the distance mostly). But for real costumes, our general thoughts are that CP would actually be more difficult to create, the clothing is very unique. The vest you suggested works well for the combine soldiers though. And we could use Hatch knee pads for the pads on the arms and legs.
I'm on the hunt for a SPAS 12, MP7, and USP MATCH. More then one if possible. For my Half Life 2 movie.
Do you have any one of these guns or know someone that does? Get in contact with me! =)