WillieJar - thanks for the link. Will that work for the 501CM, too. It states for the 503CX?
For any UK folk reading this, Amazon UK sells them too for £20 : http://www.amazon.co.uk/Fotodiox-Cam.../dp/B002KEL9T0
Also, the picture shows the curtains open. On mine they are closed if I take the film back off and pressing the shutter has no effect. How does one manually open the curtains?