Last time in Europe I stumbled across Desperados, a beer that contains tequila. At first, the concept seemed icky, but once I tried it I really liked it. The problem is that its hard to find. Made in France, distribution is somewhat limited and only in Europe.
But once we hit the streets of Barcelona, it became a primary objective to find it again. We must have visited a dozen bars, where not only was Desperados not on the menu, but they had never heard of it. Finally I found a bartender who knew it well and he gave the name of a place he presumed would have it. We headed there in anxious anticipation of finding it, only to learn that they didn't have it either. But the owner of that pub, sent us to another one, where low and behold - there it was, finally.
As a result, we consumed quite a few and it was well worth the effort to find.
So its not a margarita, but if ever in Europe, you might want to give it a shot... if you can find it.