If you have an EFI Fiery controller for your DocuColor, driver supported ended years ago and you are correct there will not be a Mojave compatible driver for that printer. For Fiery printers that no longer get driver updates EFI publishes the Fiery Express Driver. That's a bare bones PS driver giving you limited functionality. If you need more than the most basic functions then you have to setup the Express Driver to go to the hold queue and set the rest of your job properties in Command Workstation.
Fiery Express Driver Download Link
Note: If you update to Catalina you will not be able to use Command Workstation with your DocuColor anymore. It requires Command Workstation 5 which was only published as a 32bit app and those won't run on Catalina.
