And they would die eventually of natural causes anyway.
First off, lol. (I know lol is not used a lot on these forums [for some reason?] but yeah)
Yeah, but it isn't the guns causing it, it's the drug law. There are a plethora of gun suppliers in the world, they really don't need US guns, we're just close by.
Well Mexico bans guns. And we make up most of Mexico's total land border area (I pulled that out of my ass but it is pretty obvious if you look at a map), so the only other avenues into Mexico would be the occean, a notoriously obvious, inconvienent, and expensive route, or that tiny country that is their south border (guatamala maybe?). Now, look at the list of the worlds major arm exporters (take my word for it or look here
http://en.wikipedia.org/wiki/Arms_industry), you will see that only one of them shares a border with Mexico, and none of them are in South America. It follows therefore, that if the US were to, in a magic scenerio, halt all gun produciton (or limit them to only 5 bullets per magezine or some other thing that would vastly reduce their ability to kill people) Mexicans would have to import their guns across either the Pacific or Atlantic occeans.
Now small boats can not cross an occean, so the boats bringing the guns to Mexico would be pretty darn noticible. The increased cost of transportation would also increase the cost of the guns (likely in a significant way), limiting the amount of people the cartles could employ.