Brian,
This may be of interest to you if you ever get a Batavus to put out enough power.
I have not actually tried this, but cursory measurements indicate that the Batavus Starflight rear sprocket (50T) is interchangeable with a Motobecane Model 7 (39T),
Actually looks like you could use the complete wheel, I think the hubs are identical, this may offer you another source fo Batavus rear wheels.
Ron