Unfortunately, it seams I would have to wait for third party grips to come out. The only third party grip that came up for "D7100 battery grip" search was this http://www.pixelhk.com/Proshow.aspx?id=286 But they don't seam to be selling it, yet. At least I could not find how to order. I tried going through "E-order", but after filling all the required information I got "Sorry,No this product resources!"
How long does it typically take for the third parties to come up with the grips (based on D90, D700)?