If we are talking the original black and white LCD Rocket from NuvoMedia, with the Rocket icon in the upper right, it's the same charger used with the eBookwise 1150.
You want 12 volts at an amp or so with a O.D. 2.35mm. I.D. 0.7mm center positive plug.
I use a Radio Shack catalog number 273-1775 (replaced by catalog number 273-358), 12 volts at 1.5 amps. It used to come with one free AdaptaPlug. The Rocket uses tip "A" with center positive. It's a very expensive ($32) option and if you don't mind poking around the internet a bit you should be ale to find something less costly.