Probably EXDOS card is the most rare extension for the EP. Unfortunately. (EP monitor and mouse is more rare, but we usually do not want to use them.) But almost everybody would like to use an EXDOS. But there are a very few of them only. There are electric diagrams for different EXDOS cards, with or without RAM and/or ROM extensions.
But you will found a built, working one rarely, like a white elephant. Keep looking, or build one. Good luck!
You will found help for building exdos card here, if you have ambition for it.
