from 2003, that uses a 110 converter to 12 volt power supply. While none of my newer monitors have power supplies, I imagine there still might be a few out there available.

Though, a quick google search revealed that they might have extra features: http://www.12volt-travel.com/12-volt-digital-tvdvd-combo-133-inch-flat-panel-p-9796.html?zenid=8037a16f640fc74519b5a7437edcec03

It does have video inputs, but also a dvd player / tv.

Tiger direct didn't have any hits, but New Egg had two, though one is only an 8" screen and the other is designed to be ceiling mounted to keep the brats in back happy and quiet while you're on a road trip.

http://www.newegg.com/Product/ProductList.aspx?Description=12+volt+flat+screen+monitor&Submit=ENE&DEPA=0&Order=BESTMATCH&sourceid=mozilla-search