This sale is for a very good condition Mamiya C Waist Level Finder for C series cameras. It certainly fits the C220 and C330 cameras; I do not have any earlier models to test it with.
This WLF – taken from a C220 camera – is well used. There is a scratch on the dioptre and spring to hold it up is a bit weak but it is still very serviceable; not the best but it works.
This is an really sought after item – not easy to find. Just try finding another one (apart from in Japan at crazy prices, plus shipping, plus import duty, plus dodgy Japanese descriptions. Good luck with that!).