Storchpilot... you're probably referring to the TPC series charts (1:500,000). Excellent charts, provided you can fold them up enough for easy use in a small, cramped cockpit - and further provided you don't forget the scale when using your 1:1,000,000 scale ruler to check distances.
TPC charts for PNG seem to be few and far between these days. Seems there was a bit of a dispute between the Oz military, who produce the charts, and the PNG National Mapping Bureau, who re-produced them. Not sure about the current situation but my understanding is that it's in the too-hard basket at the National Mapping Bureau.
Don't know where else you'll get your hands on them as the blokes who have a complete set, won't part with them at any price.
You might find that the JOG series charts (1:250,000 scale) are still available for all those areas, but you might need a few of them to cover all the areas of your interest. There's also the T-601 series (1:100,000) that may also be still available from the NMB but, again, you'd need quite a few of them to cover all the areas of your interest.
Chart prices used to be in the order of about K20 per T-601 and something like K30 per JOG chart. You'd have to check with the NMB directly, for up to date information, but they don't answer e-mail. I don't have a phone number for them off hand but perhaps someone else, with a PNG phone book handy, might look it up for you - under the Dept. of Lands and Physical Planning, I think it is.