Pro Series Battery Power Grip for Nikon D3100/D3200 Digital SLR Cameras XTNG3100
MeiKe MK-D3100 Battery Grip for Nikon D3100 D3200 | MeiKe Store
Amazon.com : Neewer Professional Vertical Battery Grip Replacement for Nikon D3100/D3200/D3300/D5300 SLR Digital Camera, Works with 1 or 2 Pieces EN-EL14 Batteries : Electronics
Phottix Battery grip for the Nikon D3100 or D3200 - YouTube