Might try giving Honda Customer Service there in NZ a call/email.
They might have some tips, or at lease be able to refer you to an authorized dealer who is familiar with that model and can probably figure out what is really wrong.
[url]http://www.hpenz.co.nz/contactus.aspx[/URL]
Got any photos of the underside of the mower you can share?
From the small image in the brochure, looks like the blade might be in two pieces??