It doesn't take many. And you might be surprised at some of the things that are floating around.
The average citizen likely doesn't know the best aiming points for possibly encountered hardened vehicles anyway; those who've long practiced the theory and techniques of killing enemy armoured vehicles can not only best utilize the equipment involved, but are also more likely to be in a pretty good position to obtain it if so inclined. Though an *armored* commercial pickup truck should n't prove much of a challenge.
And if it comes to that, I've been in places where they were for sale in the $25-$50 range each in the right circles.