There are also some third party lenses from other manufacturers available for the NC series cameras. I know of at least two such lenses, but more might have been on the market at one point.
There are two 70-150 mm 1:3.8 zoom lenses available, one marketed by Osawa and the other by Varionar. The two lenses are basically the same, with just minor cosmetical differences. The lens design (optics etc.) itself is identical and contains 9 elements.
These lenses are occasionally available on the used market. They are usually not very expensive (under US$ 50) even in excellent condition. I got my two samples from eBay auctions.
The performance of these lenses is not quite up to the standard of the Mamiya lenses, but they are still usable. The Mamiya 80-200 mm 1:3.8 lens is much better though.