Not sure how much you need but this looks to be what you want.
While I agree with Bryan316 that phono jacks are not the best choice for 12vdc connections, there's really no danger in using them. First of all, you can't get electrocuted from 12vdc, you can't even get shocked. Secondly, the tip of the male jack (positive) touching the sleeve of the female jack upon insertion can't short anything because the current has no where to go. In fact, there are plenty of wall wart type adapters that have a 1/8" phono plug on the cord.My complaint about this concept of yours, is using phono plugs and jacks. In the action of plugging in a 1/4" phono or even a 1/8" headphone plug into a jack, is the tip actually grounds out with the sleeve, inside the jack. Ever notice a guitarist swapping guitars, and you hear that awful POP as he unplugs, then as he plugs back in? It is an innate failure in the design. In instrument level signals, the voltage is very low, and current is even lower. So all you get is a quick audio pop.
Doing a 12-volt power supply through these lamp cords, your audio pop can become sparks! Trust me on this one, I've tried, and I've blackened phono jacks and plugs when connecting while hot, and especially when they accidentally get yanked out. I cannot recommend against phono plugs for power with more urgency and caution.
All of the above examples shield and cover the conducting terminals, so they cannot accidentally ground out against each other, and you cannot accidentally touch both terminals and electrocute yourself. They're also designed to only plug in one way, so you don't accidentally plug em in reverse polarity.