Find the nearest American embassy, and then either ask them and follow directions, or go to the nearest mall and see if there's a Taco Bell / Pizza Hut place at the food court. This Taco Bell will not necessarily comply with the most stringent, culturally-sensitive rules of Mexican cuisine, but I still think you'll quite enjoy it.

Or, next time you're in Spain, you can find a taco place there. There are a lot of Latin Americans there (mostly Ecuadorians, though), and they'll probably be able to serve you excellent tacos.

There's something delightful about having to find an American embassy to find a taco place.