Liklik, I think Mal Smith's 'Airlink' was the last to run GKA-MAG RPT and that folded years ago. You will probably still find Mal at Pacific Helicopters in GKA though. Adventist Aviation Services next door or MAF over on the 'West Side' would probably be able to charter you in turbine comfort if that is something the budget can afford?!
Enjoy your visit. I hope it doesn't disappoint you too much. It is not the same PNG these days...