Tokyo Marui will be releasing the M16 Golgo 13 Custom rifle by 13 March 2009 (the 13 being the number here). This rifle is not based on any real world custom rifle but on the Golgo 13: Top Secret Episode game that is one of the more "non-family" friendly games for Nintendo. Duke Togo (Golgo 13) is an assassin whose task is to kill the leader of the Drek Group. He was an expert sniper with 100% accuracy. The game is available for the Nintendo NES if you're old enough to have gotten one of these.

Suggested price is  69,800JPY (US$772.00). Ogre doesn't dig the rifle, but I do. I like the sniperstock.