I know the post is old but this may be helpful to others. Many corn tortillas (even here in Mexico) use some form of wheat as binder. Be careful with that. Ask for tortillas de maiz blanco. Also don't overdo it because some of us do not do well with corn. Remember, most corn on the market has been genetically modified so who knows what you are eating.
Here are some stores that carry gluten-free. Caution: make sure you read the labels (of course) but especially on locally produced breads.
Bionatural (5th avenue around 40th)
Organik Boutique (Playacar Phase 2) (on fb as Tienda Organica Playacar)
Walmart, Mega, Soriana and Chedraui are large supermarkets that carry some items.
My best to all!