Treefrog,
I'm a physics teacher, about to start as HoD at Christ's College in Chch. The Head is also a physics teacher from the UK.
They have waited an age for me to arrive (not there yet...5 days to go!), because they couldn't find a suitable candidate for the job - Christ's is probably one of the most prestigious schools in the country. It's not because I am anything special, but that there must be a shortage of physics bods on the ground.
http://www.edgazette.govt.nz/vacancy.php?action=subscribe
will keep you informed about all teaching jobs in NZ. I subscribed for several months to keep my eye on what was happening. There seemed to me to be plenty of jobs in physics advertised, if one bears in mind the population size.
I didn't look at the other sciences as I'm rubbish at biology adn have only a boyish facination with chemistry!
Cheers
David