The 11th Christchurch Big Band Festival runs over Labour Weekend. There will be loads of free performances all around town by big bands from all around New Zealand and of all ages. There are also a few paid events such as jazz workshops (open to anyone), a big band ball and gala concert.
Details will be at http://www.bigbandfest.org.nz/.
Bands can also register there now to be part of the festival.
http://www.bigbandfest.org.nz/register/big-band-performance-registration-form/