Have you installed some of the repro door locks? Were you able to remove the spring from under the operating lever on the original and use on the new ones? Really if I had a key for the originals I would use them. They cleaned up and look as good as the repros. I did have the key but am now unable to locate it. Really was not planning on using it so did not secure it.
An old time locksmith can make you a new set of keys to fit your locks. Haha.......when I moved down to Texas from Colorado, we apparently packed the '57 keys in one of a hundred or so boxes. Called a locksmith, he had the blanks, and within an hour he came, picked the lock on the door, made new keys for both the door and ignition, charged me 15 bucks. That was 15 years ago.
An older locksmith shop could make you a key if you take the tumblers to them,I used my old springs no problem.