Mainframe emulator: http://www.hercules-390.org/

Yeah, it's kind of hard to get into the mainframe business. Kind of like getting into piloting a passenger jet. You can't pilot a passenger jet without a few hundred hours of flight time on a jet aircraft.

You can't just buy a used one and fly around on your own. So you hope someone who owns a jet will lug you around until you become competent and certified.