Hi. While searching for a flight from Tabatinga to Manaus I came acros your query. I assume this is an old entry and you don't need the info any more, but if not...
I've had success with a local travel agent in Tabatinga. Flights don't go out every day and they're a bit pricey.
I don't know if the link below is current. I will be setting up a flight for this summer. If you're interested, let me know. I can read Portuguese.