Airliners.net give a variety of ranges for ATRs depending on the model.
Distance Calculator - Cities Near Papua New Guinea – Port Moresby shows the range of cities from Port Moresby.
Indonesian destinations seem to be the obvious choices but the Southern Philippines or East Malaysia could come into play depending on model of ATR, how long people are prepared to sit in a turbo prop and if the operator wants the same crew to do the return flight.