It seems that Nyko is planning to release their own light gun shell attachment called "Perfect Shot". Release date is November 25th, but Amazon wont ship for another 4-6 weeks. Item sells for $14.99 but Amazon is selling it for $12.99.
Although its white and has a orange tip, there will probably be complaints from parents as the gun looks similar to a real gun if someone was to paint it all black.
Features
Traditional one handed pistol-like grip. Tactile trigger activates the "B" button
Aiming sight increases accuracy
Wii Remote easily slides into grip and locks into place
Accessory pass-through port for other attachments like the Nunchuk and Classic Controller
One hand remains free to operate the Nunchuk or other attachments simultaneously