You might be able to get a key for the switch (if original) by removing the door lock and looking for a 4 digit code on the stem of the lock cylinder. That may match the ignition key. GM used Briggs and Stratton keys from 1935-1966, and a competent locksmith can cut a key from the code. If you can't find one of those (a competent locksmith) check out this post for info on how the keys were cut.

Kevin
1951 Chevy 3100 work truck
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Photos
1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.