Yamaha CS80

Hi all:
I'm Sebastian Cordoves from Argentina, my native language is spanish,
please forgive my poor english.
I'm a recording technician, and teach music production for living.
My wife sings, togheter we have a electro-pop band. 
I own some analogue synths, and know a bit about electronics, so I do
my own repairing (everytime I could).
I bought a Yamaha CS-50 about 6 years ago, it worked well for about a
year, but then it broke up. I bought a Kenton MIDI retrofit, but never
installed it because it came a few days before the synth stopped 
working.
For various reasons I put the synth aside and only about a year ago
started trying to repair it.
The problem is the KAS, and I am almost sure that is one of the Yamaha
custom chips (YM26600 or YM26700). I don't have an oscilloscope, so
I do some metering with a multimeter and some of the pins are outputting
what I think is right data but others are dead. I have the schematics
of the CS-50 (Courtesy of Kenton), I'm in the process of scanning them,
I can post them later.
At the moment I'm driving one voice of the synth with the CV/Gate out
of my Novation BassStation Rack. I'm planning to buy a PAiA MIDI to CV
interface to drive the 4 voices, and install the Kenton retrofit to
control cutoff and other parameters.
But it will be great if I found the Yamaha IC's and remplace them.
Does anybody know where can I find those chips or even an entire KAS?
I've looked in e-bay and over the internet with no luck.
Thanks in advance for your help.

Sebastian