Try BBS timbers in Hornby,
They used to have greenheart lumber along with hardrock maple, purpleheart, black walnut, and ash.
There is plenty of yew, black locust and a few osage trees in CHCH. Talk to an arborist and he may point you in the right direction. When I was last there I saw some beautiful yew staves growing in Burnside park and the botanical gardens. There is moso growing at lincoln uni. I saw a nice osage tree in the american section of the botanical gardens too.
Good Luck
James