Hi Norm,
Yes, there is actually demand for native English speakers as teachers but it's actually a bit tricky finding the "serious" demand. I would guess the best approach in the respect is, at least at first, find a private school (colegio) that caters to expatriate families and wealth Brazilians who are preparing their kids to go to foreign universities. In my experience, there are many young Brazilian professionals with university degrees who say they want to learn / improve their English language skills. The two main reasons are (1) they want a promotion or a pay increase from their employer (employers pay more for bilingual employees here), and (2) they want to "travel to the US". The problem with this group is that they tend not to be seriously committed to English proficiency; they basically just want to be good enough to get the pay increase and vacation in Orlando (very low hurdles). Orlando caters heavily to Brazilians, so they don't need much fluency to vacation there; and the easiest way to get the pay increase is to attend a well-known English language training school (there are many here in SP, most of quite low quality) and simply get a course completion certificate (because their employers don't speak English that well and have difficulty personally verifying their English language skills).
I basically do statistical modeling and forecasting for banks and large companies (whose managers and executives tend to have Level 2 or above English skills). I thought it would be much easier to gain clients but because I am a foreigner it has taken me about 8 years to begin to be regarded as "sério", which is the primary requirement to do business here. Sério can be roughly translated as "serious", but it actually means much more: it means a simultaneous combination of capable, committed, and trustworthy.
Here's an example: My son is a native American English speaker who graduated from colegio with high scores, and strong Level 2 Portuguese skills. I know a young Brazilian woman who has, at best, good Level 1 English skills who spent 6 months in New York City in a cosmetics training course. My son has great difficulty attracting English language students, but the young woman is in demand at private high schools to teach English. What's the difference? One person is considered sério, and the other is not. So, as foreigners we must generally work with a institution that's considered sério.Â
Cheers,
John