Grover.com or google the wolfe whistle site for the proper address. They are expensive as heck! The little compressor if a hundred or more! Its not a direct drive like you see on the cheapies at autozone. It charges a tank and then you get a 12v solenoid or lanyard type valve. J.C. Whitney has some stuff too. jcwhitney.com
You might save some money by buying a cheap 120 volt compressor from Harbor Freight and use it to fill a portable tank installed in your vehicle. These are generally a lot cheaper than 12 volt compressors.