Hmm. Sounds like you believe it has to be an original Sega CD power block. I would say, probably not so.
Chances are the console has a label at the back or bottom that, among other stuff like model and serial numbers, states the power requirements: DC voltage, max. amperage, and which way the plug should be polarized (+ inside, - outside or + outside, - inside). It might for example say "9V DC, 2000mA" (which means 2A, or a max. power consumption of 9V * 2A = 18 watts).
Based on what you can find out, just trot to the local Radio Shack and pick the right power supply (and correct-size plug) for your console. They'll help you too if you bring the console with you.
Heck, I got a $10 power supply for my $2000 Roland synthesizer/keyboard that way (it came from Germany).