While the original Nikon MB-D16 battery grip is still nowhere to be found, Meike just announced their new MK-DR750 battery grip for the Nikon D750 camera (check pricing and availability on eBay, the same grip is also available on Amazon).
Update: the Nikon MB-D16 is available on eBay.
Additional information on the Meike MK-DR750 battery grip:
