G'day Spencer17,
As far as I know, there are no tuna companies operating out of PNG. The vessels and their helicopters visit various ports in PNG (and other ports in the Western Pacific) to tranship their catch to cargo vessels. The only companies still operating in that area are Hansen Helicopters (US owned) in Guam and Tropic Helicopters (Australian owned) who have recently moved from Guam to Pohnpei. The going rate used to be $US3600/month with a bonus if you last the full 12 months of the contract. The tax free bit is a tad misleading, in that they pay you and you are responsible for ensuring that any tax that is liable on it is paid to the relevant blood suckers.
Hope this helps,
MPT