I do have another amp.. hmm. Link meh Caleb!?
I'm having a harder time than I thought finding a cheap converter, but there are many options for finding 12v. Any old computer desktops laying around you don't use have a 12v power supply, usually 10-15 amps. You could also bring in a car battery just keep it charged up lol.
Pricey, but Stinger makes 40, 60 and 70 amp 12v power supplies that are good:
http://www.ebay.com/itm/STINGER-SPS40-40-AMP-HIGH-PERFORMANCE-CAR-STEREO-POWER-SUPPLY-CHARGER-/330768509336?pt=LH_DefaultDomain_0&hash=item4d0356e998
Do they make any bigger sizes like 140-160 amps