I would say try doing something where guys can be introduced to you, as the ones you meet at bars probably aren't of the best quality... As Patagonik says, they assume foreign = easy and looking for a good time (which is usually spot on! being on vacation and all).
Check out couchsurfing maybe, not exactly to find a boyfriend but the people on there organize lots of events maybe just getting out there to new venues will bring something "more potable" (hehe love that expression in Spanish! "no, no hay nada potable aca" in reference to men/women). I haven't been to one of the couchsurfing things myself yet, but what I have seen posted looked fun.
Last advice: make friends with girls who have boyfriends, and then you can meet all their friends.
Good luck.