While PD is mostly correct, the Automatic was introduced for the 1953 model year. The rocker clutch model was still available in 1953 also, but I would hazard a guess that a vast majority of the bikes sold were Automatic’s.
That said, what you need is a Wico flywheel. Wayne probably has some available after his latest major buyout of Norm’s collection. Contact info is available in the suppliers section. Be advised, flywheels are not cheap!