Have you actually broken a piece off the casting, or just stripped the thread?
If it's the latter, this is your friend -
http://www.machinemart.co.uk/shop/pr...%20repair%20m6
(check it's actually M6, I know the ones clamping it to the bars are, because, erm... )
A new, Yamaha clutch perch is �30.74 here -
http://www.yamahamotorcyclespares.co...3E665555&uid=0