the spec for the synth's PSU is a s follows:
type: Linear, triple output, regulated.
output 1: 12 volts @ 1 amps
output 2: 12 volts @ 1 amps
output 3: 5 volts at 0.5 amps.
obviously, you could use a +/-12V and another 5 volt supply, or get one that does them all. i reckon a common everyday AT style pc switchmode PSU will also do the job, but i havent tested one. an ATX one will also probably work, but youll have to figure out how to fool it into thinking its plugged into a pc motherboard first. i think you have to short a couple of pins on the big connector together to switch one on.. i leave that up to you, because i dont like switchmode supplies for reliability reasons. salvageing an old linear supply from a junked bit of equipment will also probably be a good route to go down...
be seeing you