I'm not sure about Mexico but that's probably all you're gonna find there. It's the same when I go to the Dominican Republic with my smallest dog. The food is garbage. He doesn't even eat it to be honest.
You're probably better off raw or home cooking for those six months.
The only other thing I can think of is if you find a really good vet out there and could maybe ask them to order your blue buffalo brand to their office. Maybe if you pay a little upfront they'd be willing to help you out lol. That's the only real way I could see you having access to it out there but I could be wrong.
Good luck with the move ! Sounds exciting (: