Can you speak German? If so, then try calling various German schools - Gymnasiums, etc. My boyfriend is a teacher at a school in Munich and there is a program called 'quereinsteig' or something like that - this program is for people who have Ph.Ds but want to get a teaching qualification - rather than starting over and doing the 6 year degree, they do it in 2 years. Anyway, my point with all that is if you call each school director and explain your situation, you might have some luck. You could compare it to this 'quereinsteig' program and see what they say. I think many places might not be interested, but it depends on the director of the school - and you only need one helpful person (supposedly they do exist).

Your best bet would be to search and find out where the bilingual schools (esp. Gymnasiums) are - they could use you, native speaker, as some kind of special extra that the other schools don't have. One thing to keep in mind however - there is a Fulbright program that sends over native speakers as language assistants, so some schools could already have a native speaker on site. But, just give it a try and don't get discouraged if some aren't helpful - there are a lot of schools in Munich and the surrounding area, so good luck!