It's not the same, but if you'd like to have a go at mainframe technologies you can do it with a Pi Zero: https://www.rs-online.com/designspark/my-raspberry-pi-thinks... Once you have the basic emulator setup working, check out the Turnkey system below. It's MVS 3.8 so not current Z/OS. If you google around for z/os ADCD, you might find an actual Z/OS CD to try next. http://wotho.ethz.ch/tk4-/
"MVS 3.8 so not current Z/OS." Bit of an understatement, MVS 3.8j was released in 1981.
80% of what a beginner to IBM big iron would learn at first can be done on MVS 3.8.
It's more like the difference between SysV and Linux, or Windows NT and modern Windows. Major differences and lots of features in the newer stuff, but for first principles it'll do.
Like I said, if you want modern(ish) Z/OS, ADCD is your best bet.