It’s worth giving Stats NZ a call and asking what databases they had. I called them late last year for advice on some stats and the guy I spoke to was very helpful and walked me through navigating their databases while I was online. I’m sure it will be hard to accurately measure due to the very nature of what you are measuring but worth a crack.
BTW, at Rocketspark we love supporting people doing great things about homelessness, at risk youth, health, wellbeing etc so don’t be shy in hitting us up about how we can help with your website needs if you want to have a digital presence. We’ve helped hundreds of not for profit organisations get online and help keep their costs very low as they use our website builder and we’re always happy to look at special rates for not for profits. When you are ready give the team a call on 0800ROCKET to see how we can help.