Here's some places to look:
PN 03-3293 1962-1966 NEUTRAL SAFETY SWITCH FOR MODELS WITH AUTOMATIC TRANSMISSION AND COLUMN GEAR SHIFT. $ 28.75 Contact:
How to Contact Galvin's Rambler Parts NEUTRAL SAFETY SWITCH
Both of these are the same switch as yours, but with a different backing/mounting plate. With one of these new switches, you can remove the backing/mounting plate and replace with the original one off the old switch and you're good to go.