You may have to contact Bradley for the 12 volt car adaptor. Once you get that adapter, you can take it into an electronic shop like Radio Shack and pick up a 12 volt AC converter. The reason you will need to take the other one into the shop is so they can match up the right connector, or you can pay a little extra and purchase a universal one, but be careful they call them universal connectors but some times they don't match up with the device you have.
I have also seen converters (adapters) that allow you to plug your car 12 adaptor into a 110 AC outlet.