Welcome, where are you moving back from?
I did 12 years in the UK and was part of a active car club (non BMW). We drove to Europe three or four times, attended the majority of the big UK shows, Sana Pod events in the pouring rain, dyno days, engine building weekends, club rates on parts (those days seem gone), drinking and crashing out in our cars etc. plus regular meets in the City for a vindaloo.
I appreciate NZ is a small country, but when I moved back towards the end of 2013 I quite shocked at how inactive things had become over here. The club I left had grown weeds. Everyone seemed to have packed up their s..t and moved to Facebook-land where it's easier to post pics of past events than to plan them. I attend a few things locally, Southwards cars n coffee is relatively good. The BMW Car Club also organises pub meets and weekend cafe events in the region which are good. I can't speak to membership as I haven't joined. Check out the Christchurch section of the forum and see if anything is on. Hopefully, if you are motivated, you can make some contacts and get something going. I believe the BMW club were looking for a CHCH person at one point.