Why use blueprints rather then your sons imagination? or is it as a self learning thing to model from blueprints?. Try startrek.com for trekky blueprints, and starwars.com or the force.net for star wars ones. Also try refining the google search for specifics, for example, 'Heckler and Koch mp5 blueprints' will get you to a much shorter list.

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Toolset: Blender, GIMP, Indigo Render, LuxRender, TopMod, Knotplot, Ivy Gen, Plant Studio.