Once you have a family, search the marriages for the children's marriages. Then repeat the Electoral Roll thing. Finally you will hit a living rellie that you can go and meet. Of course it is not always that simple. Some families move.
Some families leave the country.
The ones with indexes are the best. And of course there is always the chance that someone else is researching the same family. Check these for names. You can join the NZSG and use their lending library. I joined, but never borrowed anything, and decided after three years that I may as well not be a member.