As I said in the original post, where in the world are you?
what do you want to do with such an old system?
I may be able to help but I need specifics, I help maintain some of the oldest NEC systems in OZ but even I don't maintain a D3 anymore. However I am still looking after Dterm Vs though. I think I still have the Dos Programme but this is an antique we are dealing with (Ironically I do believe I have the gear to talk to even older systems, anyone remember the suitcase sised change controller for the 12 series, fortunately I have a pc version and somewhere I still have a comms card)!