Tamiya can also be found through "Hobbytown USA" (I think you can order through the web site). But I agree with IGFreely - they look horrible for WH40K use. I did once have similar inclinations as to using MP5 and AR15 looking weaps, but there just isn't anything premade yet. I have converted some IG Lasgus to look more like modern weaps - e.g. Lasgun to HK93, OCIW, etc. If you combine pieces of Tau rifles you could make bullpup style weaps - e.g. (like the Elysian Drop Troops) AUG Steyr, etc. I also combined lasguns, chimera lasguns, bolters, and tau - and mimicked some weaps resembling AK-47s and family. I am hoping to post pics at a later time.
oh, yeah - almost forgot - I mimicked a minigun using a multilas from a Sentinel. Infact, I made a man portable version, and a base mounted version (using the IG Heavy Weaps tripod), and the barrel of the chimera multilas attached to an IG LC.