I've had good luck with these people over the past two years.
America Ship
Never had a vitamin or supplement refused.
After you sign up for a free account, you get a unique shipping address in Brownsville, TX, where you have your supplier send the supplements.
Their website is not easy to navigate, and the importation process is a bit confusing. But once you do it once or twice, it seems pretty straightforward.
Shipments usually arrive in about five days via Estafeta.
Costs after shipping, handling, import duty, etc., make them competitive with Amazon.com.mx and iHerb.mx.
FWIW...
P.S. I have no connection with them, except as a satisfied customer.