Helmet model is the same for all allied forces. The model itself is located in pak0.pk3 models\gears or in models\equipment. Browse the file and youll find it. The filename is called us_helmet.skd. You can find the path also by looking at one of the allied mp player tik files also.
Helmet texture is in pak2.pk3 textures\gears or something similar. A webbed helmet filename is something like blanc_web.tga.
And btw, on more thing, I want to put a knife and grenades on the Stock airborne, what do i have to do with the tiks and where do i put those knife and nade ?