You may already have searched UA and seen there's lots of availability in economy to a number of the islands with Air NZ, especially March April (I didn't search further). I think the transfer rates of Marriott to NZ and UA are a bit pants? but you could use your UA miles at least. No idea if it's a good or bad redemption but it saves you $
I did seen an article on Australian frequent flyer regarding using SQ miles.
https://www.australianfrequentflyer....iti-krisflyer/ I've had issues seeing NZ on SQ searches but you can double check award availability on expert flyer. I for business, A for PE and X for economy.
You may need to look through the redemption charts of some of the other *A programmes to see who has the best value to transfer miles as availability isn't the main issue here.
Could use BA for Qantas. They're starting flying to Fiji.
Could transfer Marriott or AMEX (don't know who your transfer partners are) to AA to use on Qantas, Fiji airways, and Air Tahiti. Can't comment on availability though so search that first. Tahiti flights might be a call up job but there was an article by OMAAT on this.
Virgin Australia also have a reasonable network to some of the pacific islands with some originating in Auckland. They partner with Delta and some others. No idea about availability or redemption costs. You could transfer Marriott into a VA partner that's going to be useful to you in the future. Maybe Virgin Atlantic? Or directly into VA if better availability. Just an idea, I haven't looked into the details. Easy to keep VA points active even abroad until you can redeem for a partner flight.
Cash fares there's also Air Nauru? to Norfolk (or NZ from Brisbane and Sydney), and Samoa Airways to Samoa to compare. Agree with using the NZ websites to look for fares on Air NZ.
I don't know if this is useful but apparently via travel agent
https://www.allairpass.com/wp-conten...th_pacific.pdf But travel agents may have more ideas about passes etc.