I live in Costa Rica, and I spent two years in Brazil. There are many Spanish language schools here, but I've only met one non-Tico teaching Spanish. I would expect some problems. Why should they hire you when they can hire their cousin or neighbor? Each country seems to believe that its brand of Spanish is the best, purest, etc. That is yet another prejudice. Forgive me for being negative, but these are attitudes I've seen often. The "argolla" concept is very strong in CR. What you know is not as important as whom you know. Don't forget visa requirements. Some teachers are clearly working under the table, but getting a work permit in most countries will be next to impossible.
You will be able to find the names of Spanish language schools at many tourism websites. The next time you are in the D.F., you may want to try the embassies, asking to use their telephone books and read newspapers from their countries. If you can find something in English (such as The Tico Times), that would be a big help. Foreigners read them, and there will be ads for schools. A large number of schools in CR are located in beach communities. The idea seems to be that students can play in the surf when not in the classroom. I don't know if this is true elsewhere.
Good luck. You may need it.