Someone's been drinking to much Starbucks:
First, face up to where the Mexican cartels get their weapons of death. Virtually all, including pistols, grenades, high-powered ammunition and assault weapons such as the AK-47, are smuggled from U.S. territory, across the border into Mexico, where the gangster elements pay premium prices for them.
Yep, I can walk into any gun show or shop in the US, grab a couple AK-47's and a satchel full of grenades, and have them shipped FedEx to Mexico for some quick bucks.
Maybe, just maybe, the "pistols, grenades, high-powered ammunition and assault weapons" are coming from the "notoriously unaccountable, often corrupt, Mexican military and police forces".
But that would make sense, now wouldn't it?