Airsoft Atlanta have sent over details of the M870 Marui shotguns they are stocking:
Airsoft Atlanta has the Tokyo Marui M870 Gas Shotguns in stock. 3-shot full sized shotguns, featuring a metal barrel and full metal receiver. Also available, rare spare gas tanks for the M870 and extra shotgun shells (green and white variants). Come check it out at:
http://www.airsoftatlanta.com/Tokyo-Marui-M870-Gas-Shotgun-p/13843.htm