I guess you could always go back to electromechanical relays. I wonder if it might be possible to come up with a method of 3D printing those? But in practical

I guess you could always go back to electromechanical relays. I wonder if it might be possible to come up with a method of 3D printing those? But in practical terms the Z80 was a 4 um process node so unless you're willing to go back to the proverbial stone age it seems like you need semiconductors and lithography.