IBM had the opportunity of being the royalty-free ISA that RISC-V is. Or even release the cores "IP". They squandered it.

There are at least three open cores, all IBM funded or designed:

https://github.com/antonblanchard/microwatt https://github.com/openpower-cores/a2o https://github.com/openpower-cores/a2i

The last two are older but they work. Microwatt is developing by leaps and bounds.