John
you can make your own..simple:
4 pin DIN element 14, nice plug OEM, $14.66
4 Pin Din cheaper element 14, $3.34
4 pin DIN RS components. cheap good has removable lock cap, $5.76, free postage.
All you then need is wire (thick'ish gauge) and power connector (preferably fused) to power supply. Manual shows which pin is which power wise.
Both power sockets on the Gemini 1 are connected in parallel. As looking at the power sockets on the Gemini, the 2 right pins of each socket are earth, the 2 left side pins are +ve 12~18V DC power in.