It could be worth a look - as, many years ago, on my old cb750F1 I used GL1100 clutch cables and throttle cables to fit high bars. The clutch cable was a bit thicker than the 750 one but a bit of ingenuity made it work.
Necessity is the mother of invention, as they say...
You may need to adjust free play with spacers or adjustment but it might work; I used to have a friendly local bike shop spares man who would let me take my original cables in to him and he'd see what had the same ends and similar free play but a bit longer overall. You can but try.......
Failing that there is a cable company called Venhill who will make to order, just send them your old ones and tell them how much bigger you want them...
http://www.venhill.co.uk/