My advice would be not to take everything you read on PPrune as gospel. PNG, Cape York and the Torres Straits are beautiful parts of the world in their own right, living and working in these places may cause people to become jaded and biased against them.
I would have thought that with a good amount of planning, anything would be possible. PNG obviously has its difficulties with Avgas but that's not to say it can't be done. Some research into options, potentially having 3 or 4 205L drums forwarded for you by one of the aviation companies and stored by one of the local shipping companies (or a local company run by someone you can trust). Everything is for sale at a price. Of course, there will be hiccups so you better be prepared to wait a while or pay a lot, but I would just about guess that it would be the most memorable flying trip of your life should you go. You'll just need to do a LOT of research, both cultural and logistical.
FWIW, I'm talking about the coastal regions, Milne Bay and New Britain, not the highlands BTW.
If you were determined to do it and stated as much. I'm sure you'd get a lot of help from those on PPrune with contacts in PNG.