what agedambush said, in doc Mitchell's house on the table behind the stretcher or you can open the console and type in player.additem xx000800 1 (xx=the esp. files position in your load order)
I really love this gun but my problem with it is that its TOO powerful. When I can hit anybody on very hard mode in any part of the body and they instantly go flying 10 feet back then its not a balanced gun. Needs some balancing issues worked out but otherwise its great.
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It's supposed to be in "textures\m110\m700\", but that path doesn't exist.
(xx=the esp. files position in your load order)
Hope that helps