Hi - I'm not sure how old you are, but my 17 yr old is heavily into basketball and since moving to ChCh a year ago has had more opportunity to play than in Auckland. He plays with slightly older guys but has met most of them through college.
There seem to be a few different leagues & loads of basketball courts around.
Some contacts are - Kiwi Hoops.co.nz - Web site dedicated to New Zealand basketball; carries the latest scores, statistics & points tables, journalistic columns, interviews & profiles; based in Christchurch
www.canterburybasketball.co.nz -Non-profit sporting organisation to foster the growth, development & promotion of basketball in Canterbury; manages all club & social competitions; operates an extensive junior development programme for age group players in Canterbury