I've never seen a street organ in Holland turned by hand except for
special occasions or in museums.  The standard power seems to be a
small Honda generator which operates an electric motor.  This drives
the large flywheel via a cloth belt.  This belt is flexible enough to
conform to the curved flywheel.  I've never seen this type of belt for
sale in the U.S., by the way.

Philip Jamison
West Chester, Pennsylvania