Beachbunny I dunno what you mean by getting the CASA to endorse your licence. The most logical thing to do would be to get a PNG licence if you are going to fly there,it's relatively simple if you follow CASA's guidelines.
They also have a website now
Civil Aviation Safety Authority of Papua New Guinea check that out and if in doubt you could even email or ring them.
There are also rumours going around that CASA have started doing random ramp checks. Good to see as this has been well overdue,