A Google Search on "Bespoke Clutch Cables" yielded:
http://www.venhill.co.uk
http://www.speedycables.com
http://www.rdb93.co.uk/

Worth some 'phone calls - but beware sending your broken cable off in the post - 20+ years ago my father sent a clock component off to some people and when he called by to see about the delay, the shop had collapsed into its cellar!

Good luck.


Paul
Costock, UK
Plus Four 75th - Furka Rouge - Pip
Disco 5
Teddy - 17h1 Irish Draught cross