check out California Software baby iseries.
Not sure why anyone would need it today but
each to his own.
No such simulation software exists outside of (perhaps) IBM. There was a product from California Software that could run most RPG programs (not RPG IV and not ILE) and many CL commands in a kind of simulated environment, but it was neither useful nor appropriate for training and demos. It would be cheaper to buy a used AS/400 than to buy software to simulate one; and you wouldn’t be running a simulation.