gday mate, belive u me understand that problem alll to well, from what i understand of NZ native trees, they have the potential to be as dense as some of the aussie trees so dont fret, use what you can find in your local tmber shop a good way to go would be spotted gum (i donno if u have it there) but also check out
www.ozbow.net its just like this site but for aussies since we "officialy" have no osage, yew ,hickory,lemonwood or any of the traditional bow woods but as you get more and more into the loop with your local timber groups you may find that there is SOME osage around, i recently discovered that australia has some osage and hawthorn arount the old seatlements, brought over by american settelers (thanks guys) see you on ozbow mate!