The standard *A RTW does not have a premium economy option, however you can purchase an economy RTW and pay a surcharge to upgrade to premium economy on Air NZ (on sectors that offer premium economy). Depending on when your trip is this could include Asia-AKL-SYD/BNE/MEL-AKL-LAX-LHR but would be stuck with regular economy for the other sectors.
There are NZ/VS/SQ RTW products, but I havent seen one specifically for premium economy. The business version is a little cheaper than the standard *A RTW, but of course more restrictive.
Another option, would be to buy an economy RTW and upgrade some sectors (presumably the longhaul ones) using miles. However this could cost a lot of miles, and at the moment only NZ points can be used. *A is rolling out *A-wide mileage upgrades but NZ is not yet participating and we dont have a date for when they will be. In any event, as few airlines have premium economy, it is likely only NZ points could be used to upgrade economy->premium economy (other points would be economy->business).