Not sure if Southern wings take casual students part time or not. Someone associated with them might know but i would think most of there students are full time doing the full course
Its also worth having a look at some of the flying clubs around Auckland. People often complete their training there part time and the flying rates are often cheaper than the flying schools
At Ardmore 2 clubs
Airline flying Club
airlineflyingclub
Auckland Aero Club
Auckland Aero Club - An unsurpassable training record that spans over eighty years
At North shore airfield
North Shore Aero Club
North Shore Aero Club