I'm glad people still remember this project. I have to get get back to it one of these days, before
GW invalidates the
IG codex.
http://www.pbase.com/kidkyoto/swat
I've been using 1/35 scale model weapons since at 2000 when I got back into
GW. 1/35 is strictly speaking too large for 28mm but
GW guns are so oversized the 1/35 stuff blends right in, heck it even looks puny next to a las gun.
Anyway what I used was Dragon Quartermaster Series weapons, boxes filled with M16, H&K or AK47 varients. You can get them from online or B&M model shops. There are also WWII sets out there from Tashima, Italiari and Dragon.
I used Catachans since Cadians have their left hand molded to the darn gun! But I hear with careful cutting or buying bits from the war store you can get enough left hands to do something like this with them.
I have Dragon's M16s if you want a picture of them.
The Assault Group also make 28mm 'chunky style' modern guns.
http://www.theassaultgroup.com/