What I have done before with an unobtainable power supply, is substitute a completely different one.
At the end of the day, it only needs to supply a few voltages (they even label it so you know what they are)
So first power it up with a bench power supply (you may need several) to determine the current requirements for each output.
Source an alternative generic power supply.
You will need to figure out some switching so the standby functions work. I used the "on" signal from the main board to switch a relay, via a transistor.
I did this on a Bauer XT32 a while back as the original PSU had a well known habit of self destructing, and I wanted something more reliable.