From GameWatcher: “Chicago Typewriter is a mainstay weapon in more games than we can keep track of, and Remnant: From the Ashes is one of these games. This high-capacity sub-machinegun is a real boon when dealing with numerous weak enemies, and here you’ll learn how to get it.
It just so happens that the Remnant: From the Ashes Chicago Typewriter location isn’t in a fixed spot. Instead, the only way to get the gun is to come across a special event that appears randomly. Make sure that you carry a key, because the SMG is behind a locked door after the event is over.”
Source: N4G PC Remnant: From the Ashes – Chicago Typewriter Weapon Location Guide