You don't have to start out with blasters. In fact many groups aren't allowed to by their administration and so use balled up socks instead. I founded BUZAN (the HvZ group back here at Bristol University, UK with no previous knowledge of Nerf and a group of 10-20 people. Few years later, we're well established and have amassed a huge collective arsenal, spawned a spin out tactical gear company and have just shy of 100 members. Build it and they will come.
If people don't have blasters, run small, indoor games with a variety of game-types using socks and the few blasters you have. People will readily trade up when they see you rocking around the room with your Tacticool Stryfe.
For rules and the like, I believe the BUZAN committee maintain theirs at their website (http://ubu-buzan.tumblr.com/rules
) - a number of groups here in the UK have already borrowed them and adapted them to their specific sized games. They're different to the standard HvZ rules but work perfectly for smaller, indoor games with groups that are just starting out.
Get some friends together, borrow an indoor area (sports hall, SU building or similar) and run a few games. I dunno how New Zealand works but parks tend to work if you can't get an indoor space. Just remember the basic rules for HvZ (don't get it banned, don't be a douchebag etc).