Even if you can't find an image of troops, make a troop clone (i.e. one you can duplicate a hundred times and it won't take away from the realism of the image), and render some "up front" soldiers in different poses, slightly different clothing, faces, etc. For each render you do, save a silouette picture, with the figure white and background black, open up Bryce, click on the picture object icon, configure the texture map, along with the trans map, and voila. Its there.