if you have a valid subscription, you could probably download the ACS v5.8.1.X release / ISO from https://software.cisco.com/download/home/286304481/type/282766937/release/5.8.1.4 We did us that to create a VM, restore the data, and test upgrading from ACS v5.8 to the recommended ISE "device management" (i.e. the new TACACS+) feature.
However, when we wanted to upgrade our ACS v5.8 a few years ago, we found we could not re-use the hardware for ISE Device Management (ie. the "new" TACACS+ server). We had no choice but to upgrade our TACACS+ cluster to SNS-3595-K9 models for ISE v2.X (now ISE v3.X). Those go SNS-35XX-K9 models go EOL in a few months, in June 2024 IIRC. That would mean if you wanted to to replace ACS v5.8, I'd think you would need to move to SNS-36XX-K9, the latest SNS-37XX-K9, or VMs, plus ISE v3.X. Also, from our own research, we're seeing the "VM" license and VM software support for 3 -5 years to be far lower than the cost of physical units, so we are investigating moving some, possibly all, of our appliances to virtuals, especially for the v3.2 zero touch provisioning.
As for what you can do with old ACS units, I think we repurposed our ACS chassis with Ubuntu in our lab, to make devnet boxes. They run fine for that, even without a support plan. I'm not just doing python on them, but also writing some nodejs based web tools to allow for faster TOC/NOC type data gathering when devices have problems.
Regards,
David
