See also Immigration New Zealand's general requirements for obtaining a police certificate.

Specific procedure for Papua New Guinea

A written request for a character check should be addressed to: 

National Criminal Records and Intelligence Office
Royal Papua New Guinea Constabulary
PO Box 85
Konedobu N.C.D.
Papua New Guinea

You should provide:  

1. full names and former names
2. date and place of birth
3. present address
4. all former addresses
5. years of residence in Papua New Guinea
6. a self-addressed envelope with return postage. 

A fee is payable.