Where do I find a rotary 3 speed switch for for a window box fan?

Try an electronic or electrical components supplier like Maplin or RS components. You won't be able to get the same switch as no doubt, it went out of production years ago but you may be able to get a modern one with the same current and voltage rating. Your problem then might be fitting it to the existing fan housing etc - the holes will be different etc - might be better off getting a new fan - after 40 years the bearings must be well worn.

JD
October 2008