I have absolutely no idea where where I can purchase a live grenade. However, living in a rural area, I'd have no trouble finding people who know how to make explosives from common (and cheap) farm materials. Hell, I was making blackpowder when I was 11 years old.

Now add to that the fact that in the US I can buy a used car or pickup truck cheaper than I can buy a cheap GPS-equipped model helicopter and I definitely know which option I'd be more worried about.