I need to replace the cable on the 906, which has 3 wires.
Are there suppliers of meter lengths of suitable stuff?
Requirements:
10mm diameter of outer sheath
3 conductors, 18 gauge or equivalent (there are 30 copper strands in each, 0.2mm diameter)
Oil resistant
Temperature rating 90 degrees Celcius.

I am assuming your cable is completely rotten and it is falling apart.

on my SS Special (same basic engine as in the PASO 750) the insulation of the single cables started to crack

after some repairs and replacements I though I got to the rooth of the issue i.e. oxhidation had reacted with the insulation and I though my repair was sufficient.

few years later I was checking the voltage at idle before the regulator and noticed it was "zero", started investigating and realized that also the insulation inside the generator case was rotten and since the cable is tightly held by a ziptie, there was a nice short circuit and all windings of the alternator/stator where in bad shape.

I ended having to replace the whole thing.

in other words, it seems that with age the wiring insulation will perish and if it is not too late all cable will need to be replaced down to the stator hoping it is still good

I have a friend who had the same happening in 3 different pantah engines (all 600cc) and never once did he manage to rescue a stator, unfortunately.

Just one more thing to note. If the wiring to the stator is cooked then so is the stator.Best to have it rewound or replaced along wth the regulator.