Direct TV 12V receiver

If the receiver is Direct TV compatible, then you will have to call Direct TV and speak to someone in the Tech side, explain you own your own receiver. They will have to approve it and send you a card that will work.

A cheap inverter will do the trick. 25 bucks shoul do it easily.

With no more power than a satellite receiver draws, the simple way to go is just use a small 200 or 300 watt inverter to power it. Trying to find another receiver that "might?" work or have to alter it to make it work sounds like a waste of time.

I dont know of any 12 v systems however one could be made if a decent radio/tv repair person tackled an existing unit.. Most electronics operate on 12v anyway within the system or just buy a converter from 120v to 12v power supply.
Now that isn't the problem. The problem is your HU card is married to your current receiver. It will not work in any other receiver. If you plug it in to another receiver you will get a call EXT 722/ display. You then plug it back into your receiver and you will get decrypted signal. DTV got a grasp on their cards when they were crackable in the past with the current HU card.
Your basically out of options except for the above.

This sounds like a really bad idea. No you can't use your card. Why not just put in an inverter and use regular 120v stuff?