Amazon ships to international addresses. Granted, they don't have a big selection, but they have a few things:

http://www.amazon.com/s/ref=br_ss_hs...0&Go.y=0&Go=Go

There's always Ebay. Many sellers on Ebay will ship to Mexico. Looking on Ebay, someone has some really cute Backyardian Pjs for sale.

Good luck!