You can probably leave the inner surface more or less intact and treat it as though it was the flat surface of a Dan type profile bent into a curve. It would probably work just as well if you made it symmetrical about the centre. The main thing is to have the thick bit about 30% back from the leading edge, a sharp trailing edge and a reasonably worked curve down to the leading edge with a small nose radius.
Whether you work from the inner surface or the mean line will affect the angle that you need to cut the section at.
If you want to be clever about it you can almost certainly find details for NACA sections with curved mean line but you probably have too many variables to hope to get the results you need by other than inspired guess or trial and error. The pitch angles ( based on the line joining Le to Te ) will be very different from those required by the usual flat Clark Y sort of shaped blades.
This may give you some sort of idea.http://www.thebackshed.com/Windmill/articles/ChineseBlades.asp
Flux
