In Search of Mills Lock and-or Key(s)

[Jim]

I obtained an original Mills lock, pictured, without a key...
On the back there is a "C3" code; unsure if this correlates to a key code, but was hoping to get a few Mills Collectors to check their keys to see if an original key has any type of code on it...
If so, we'll need to verify the lock has the same key code; if it does correspond, then I just need to locate a "C3" Mills Key...
Thanks !
.