My understanding is that a drill rod blank works pretty well for the clutch push rod. Drill rod can be bought by several types: oil, air hardening, or water hardening.
I'd think an industrial supply place can get it for your need.
Over at
www.kawasakimotorcycle.org
a forum member "Kopcicle" has been using drill rod for quite a while on the many "J" engined bike's he's had.
