I am faced with a similar problem. I've become associated with an orphan school in Kenya that is currently using the traditional three stone hearth. I want to advise my African partner on how improve this. We have almost no funds for this and so I am asking about local material like stones. (I need him to send me a picture of the stone kilns they use for pottery.) I've been researching the technology behind rocket stoves and how best to adapt to local conditions.
A note for Kevin: I have found in my research that a smooth chimney throat is less effective. Turbulence in the fire column gives more complete combustion, a square stack of bricks will give a more complete burn than round stovepipe.