Go to the nearest general store and see if he spawns a cutscene. Then check your satchel

From my understanding, it’s always gotta start at the Saint Denis postal shop. If there’s no marker on your map, look for letters you have in your satchel or mailbox. Read each of them, looking for “business proposal” or “letter from Cripps.” See if a mission spawns at that specific post office.

As @444neptune was saying, you have to go to a general store first. I went to the Valentine one first and got a cutscene, so I don’t know if that’s the only place you can get it but it’s probably your best bet. Cripps will come along and tell you about a business opportunity and say that he’ll send you a letter with the details. After that you can get the letter in the post office and buy the butcher table for 15 gold. That’s when the role begins.