Kudos to cubiclekeys.com
My 54 year-old Overlander came to me with only one original key to operate all three exterior access doors all keyed to the same Chicago Lock Company tumbler plus a dodgy duplicate. I broke the original key the other day and found that the duplicate just was not going to work with the fridge access door.
So I went to cubiclekeys.com where, although a match was not immediately found for the key number, the site encouraged me to contact them. After a quick email interchange, I sent Mike a picture and he said, "Oh - look up the Anderson-Hickey number". That was the ticket - Thanks Mike!