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.
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Tim
'66 Jeepster Commando w/GM HT383E/4L60E/Atlas II/D-60F & D-70R
'70 Wagoneer w/Buick 350 V-8
'73 J4000 w/GM L31/700R4/NP-205/D-44F/GM 14 Bolt
http://jonesys.com