You can make your own or order a new from Sound Devices. Any adapter giving about 12V at 1,5A will be fine. The contact is a standard one, available from various electronic supply houses or from SD, not very cheap though. It is quite unforgiving to solder it together, quite small inside, so unless you are very used to soldering I would recommend getting a ready made one.
(For details on connector name and voltages check the manual)
One alternative in the mean time is to look inte a video supplys store. They probably sell chargers for the Sony video camera batteries the SD unit uses, allowing you to place the battery in the charger and charge it there.
Gunnar