My latest "white whale" search is a book I read back in the late 90s (I think) that I'm trying to track down, but for some reason is eluding my Google searches.

I thought it was called "The Fourth Horseman" but that doesn't appear to be the case.  What I can remember (fully acknowledging my memory might not be correct) is that it's set in New Zealand (most likely Auckland), so I think it would almost certainly be a NZ author.  I think it was set around the late 80s, built on the concerns/fears about nuclear war impacting on NZ because of visiting US nuclear powered/armed vessels.  I think the plot begins with a nuclear war starting, and while NZ wasn't directly targeted it is affected by the fallout (both figuratively and literally).  I think the protagonists are children (maybe street kids?) who have to deal with the impacts of a country that is now cut off from the world, the rapidly-approaching nuclear winter, and the breakdown of society.

I think I borrowed it from an Auckland library - possibly Massey University when I was studying there in the late 90s.  

My googling comes up with the suggestion "Children of the Dust" but it sounds like it's not set in NZ, and also it's published too late for what I remember.  It's also not Under the Mountain (I clearly remember that story, and it's completely different).  It's also not Tomorrow When the War Began (have those books, different story).

Does this summary ring any bells for anyone?