Apparently the original poster doesn't have an IQ high enough to use Google and find out that you can legally buy these for less than 50 dollars, there are no laws against selling the devices. USING the device for anything other than personal security would probably be illegal though. It's like a gun, you can buy them anywhere, you can't go out and shoot people at random though.
If you search hard enough I'm sure you could find security sites that sell GPS spoofers, which actually transmit false GPS data, the signal a GPS receiver gets is incredibly week so it doesn't take much to swamp it with a different signal even with low power levels, especially if you know the location of the antenna.
Google, learn it, live it, love it.
Oh by the way, you could also just find the antenna on the vehicle and cover it with tin foil...
Sometime I wonder how the human race can survive when we're not able to think of the most obvious things, then again I've made my fair share of 'WTF would you ask that for' posts.