Dec is going to be tough, particularly past the 15th. Best bet is to look for flights through SIN or TPE or BKK, start with OW flights from there. SQ has flights to WLG through MEL but can also connect through either SYD, BNE, or CBR (1stop) to NZ flights or book a LCC to AKL (jetstar is decent for a shorter tasman flight, most NZ flights are econ only anyway). BR also has flights to BNE where you can to the same thing via TPE.