The over 16 segment issue seems to be a problem confined to AA. I don't think a TA will have any difficulty issuing the ticket.

Personally, I have used www.travel.co.nz and they have mailed me the ticket and the Flight Centre office at AKL airport. They would need a copy of your credit card and passport with a signed authorisation. I've arrived at AKL and walked into the office unannounced and left an hour later with my Oneworld 5 continent ticket for departure the next day. Remeber there is no advance purchase condition in the South West Pacific.

If you want the name and email address of someone at Flight Centre AKL airport, email me.