My favorite LGS is only about 6 blocks from the local UPS hub. There is a brown truck that pulls up almost every day and they carry in several handtruck loads of guns and ammo.
It wouldn't take too much advance scouting to figure out which truck, hijack that truck and take it to a different location and off load the guns and ammo. It wouldn't be a big haul, but if you got lucky and did it on the right day you could get a lot.
You'd probably have to be quick as I wouldn't be surprised if their trucks aren't equipped with GPS tracking and someone would probably notice a truck off course and notify the police.