Those PS-520 cables are very rare and hard to find. You may end up having to make one (if you can get the parts).
Here’s a blog of someone who made his own cable to return a M-520 to standard after a previous owner had done a hardwired link from the PSU to the mixer (presumably after losing the cable and not finding a replacement).
http://rainbowjoe.byethost9.com/Repl...dCord.html?i=1
Though some butchering and a hardwired link may be your only option as those Hirose connectors are also very rare now. Canford Audio in the UK sell Hirose, but they only have the current range of round connectors in stock.