You could, in theory, run code generated by your own compiler on a PPC chip you designed and built with your own hands and brain.
Random thought: would it be feasible to implement PPC on an FPGA, as has been done with RISC V?
Anyone know offhand what’s the most powerful PPC system you can readily buy? I’m guessing it’s one of the PPC Mac machines.
Admittedly the latter is a $15k machine, which is perhaps may be pushing what you had in mind for "can readily buy", but it's for sale...
The T2 is a great machine, though. There's just no comparison to the Quad G5 sitting next to it. It's quieter, it uses less power and it doesn't feel like I'm lacking for CPU. I got a lot of wear out of the G5 and I'll never get rid of it, but if you don't need 32-bit and/or to run OS X on the metal, the best Power workstation is a Raptor.
https://en.wikipedia.org/wiki/PowerPC#32-bit_PowerPC
... Xilinx, FPGA maker, embedded PowerPC in the Virtex-II Pro, Virtex-4, and Virtex-5 FPGAs
https://en.wikipedia.org/wiki/Virtex_(FPGA)#Virtex-II
... Xilinx introduced Virtex-II family in January 2001 on 150 nm process technology,[14] and Virtex-II Pro family in March 2002 on 130 nm process technology.
The actual silicon-proper, not sure, but one could definitely implement the ISA.
If I'm not mistaken IBM haven't given away any actual synthesizable logic to use.
If not, there's at least https://github.com/antonblanchard/microwatt
And the most powerful POWER system you can buy would be something based on the POWER9 processor.
Why not? It is well specified so should be quite doable.
Your best bet is a VAR (that's how I got my POWER6 when IBM wouldn't sell me a POWER7), or a company like Raptor, who actually sells retail.