Actually you CAN own a .22 in mexico. It's just that it's heavily regulated. Obligitory wikipedia link and quote.
" Weapons may be kept in the home for security and legitimate defense of its dwellers. Their possession imposes the duty to manifest them to the Secretariat of National Defense for their registration. For every weapon, record of its registration will be issued."
And a secondary quote from wikipedia
"Under these two articles, private citizens are generally restricted to semi-automatic handguns or revolvers of a caliber no greater than .380 (for home defense),[28] rifles no greater than .22, and shotguns no greater than a 12-gauge (hunting and shooting when a member of a club). Anything bigger than those calibers is considered for exclusive use of the military and strictly forbidden for civilian possession, as defined by Article 11 of the Federal Law of Firearms and Explosives.[29] "
As far as I know, Aguila Ammunition is still manufactured in mexico, including .22 LR.
So the 100% Mexico ban you stated is little less than 100% imho.