A 12v-110/60 inverter and a 12v battery pack will do you. Radio Shack or an auto parts store.

But do check the shutter's speeds. A couple of years ago I bought an oscilloscope camera with an Ilex #3 Electronic much like yours but with a marked high speed of 1/125. The equivalent of your Speed Computer's internals are hung all over the camera's interior and I haven't yet got around to cutting metal so that I can rearrange them more compactly. Even so, my junk functions but the shutter speeds are all very very much slower than nominal.

Good luck, have fun,