Update: I guess I missed this product release - it has been available in Europe for few months now (still not available in the US or Canada).
A reader emailed me this link - a new product from Nikon currently only available in Germany and few other European countries. The PDK-1 is basically a power kit: it includes the MB-D10 battery grip, BL-3 adapter, EN-EL4a battery and MH-21 charger (for use with D300 or D700). No word for now if this package will be available in other countries. Price in Europe: EUR 381 (around USD 492).