What power supply do I need to use the Sure Electronics T-amps in a car?

You could, if you were so inclined, build a PWM or SMPS to increase the 12 volt power of your car's electrical system to something closer to 30v. You would get more power that way.

The simplest thing would be to hook the amp up directly. It will work at 12 volts, though the power will be pretty low... around 10 watts per channel.