I think getting your hands on the most recent versions – such as the latest z/OS 2.5 – is a lot harder, unless you work for IBM or an IBM customer, or you know someone who does (and who is willing to help you out, an action which may involve some risk for them). In recent years IBM has added hurdles to make unauthorised distribution harder (such as encrypting the ADCD distributions), although those hurdles are not insurmountable, they just add more work (usual story with DRM). And I think you'll find Hercules will barf on the latest versions of z/OS anyway.
If you want to latest versions from IBM totally legitimately – IBM will sell you a development environment (zPDT) for US$5,540 a year. If you need it for work, could be a totally reasonable investment. If you are just doing it to muck around – well, that's an expensive hobby, although certainly there are people out there who spend more than US$5,000 a year on their hobby, and many people here earn enough they can afford it – but you'd have to really enjoy it for it to be worth it. I doubt there are many people out there who enjoy z/OS that much – although there is one retired IBM guy in Orkney, Scotland (Colin Paice), who does, and he's actually blogged about how he forked the money out and bought it [1].
[0] I think it is better not to say where publicly, in part because doing so draws attention to those places and attention might result in IBM issuing takedown notices. If you know the right search terms it is easy to find.
[1] https://colinpaice.blog/2020/06/29/getting-z-os-installed-on...
One thing I noticed – IBM does not want individual consumers as customers, only enterprises. If you say they live in the US, the order form says "IBM products are only available for commercial, academic, public, research, or other organizational use", and asks you for an organisation name. I am in Australia, so I give my country of Australia and home address, it then asks me to certify I am buying it for a business, and won't let the order process continue unless I tick it. For Australian orders, it also asks for an Australian Business Number (ABN), which you get from the government when you register a business with them. (Government agencies, and educational/religious/charitable/nonprofit/etc institutions, and trusts, are also eligible for them.) I guess the US equivalent would be an IRS EIN, or a DUNS number, but the US order form doesn't ask for one, just an organisation name.
Anyone in Australia, can get an ABN, but you have to tell the government you are running a business, and in theory they can revoke it if you aren't a real business (and occasionally they actually have). However, another way to get an ABN – anyone can incorporate a company, and when you do you get an Australian Company Number (ACN), and anyone with an ACN is automatically entitled to an ABN (the ABN is just the ACN with a couple of checksum digits prefixed). I actually own a company, which does nothing and has never done anything – one day I was daydreaming about starting my own business, so I created a corporation, and then I daydreamed a bit more, and then I parked the idea – but I pay US$200 a year to the government to keep my corporation alive, so I have a legitimate ABN to give them through that. There is no legal requirement for a corporation to do anything, a "shelf corporation" which stays forever dormant and just pays the annual fees (and engages in a few other pro forma annual legal rituals) is legally just as valid as a billion dollar company
If I gave them my credit card number, and let them charge all that $$$ to it – I expect they'd process the order. How are they supposed to know that my "business", despite being a real legal corporation, is actually just a "fantasy daydream business" not a real one? I don't see how they could tell. (I mean, I could be an independent contractor/consultant/freelancer working through that corporation, rather than a full-time employee – and maybe one day I shall be.) They could cancel the order and give me the $$$ back instead of fulfilling it, but I'd be surprised if they did that.
Indeed, ex-IBM employee Colin Paice in Scotland reports successfully buying it from them – https://colinpaice.blog/2020/06/29/getting-z-os-installed-on... – I guess one thing that may help – don't say it is for a hobby or personal use, claim it is for a business (which if you think about it, doesn't even have to be a lie – tell yourself a story about how you are going to use this to develop software to sell people, and if you believe your own story, that makes it true – who knows, believing in it might even make it happen – and if it doesn't ever actually happen, well a lot of businesses fail, often even just as they are getting started...)