You can find a list of the paints used on Cub Cadets here:
http://www.onlycubcadets.net/forum/showthread.php?t=19
Most auto parts stores that carry paint can mix up a small batch of touch up paint based on the codes. No guarantees that a 50 year old paint job that has faded and is now very dull will match any new paint though. You can purchase the spray cans from most Cub Cadet dealers.
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The Collection, so far: Cub Cadet 100(x2), 125(x2), 123(x2), 70, 71. Adding more when I can find them.