For the most up-to-date maps of PNG towns you need look no further than the nearest telephone book. It features a colour map section that covers all the major centres and it’s free.
Country maps There are two country maps of PNG that should be available to purchase online, if not necessarily at your local bookshop. Hema Maps’ Papua New Guinea (1:2,167,000) 3rd Edition (2004) is the most common, and is readily available in PNG as well. More recent is ITMB’s New Guinea (1:2,000,000), published in 2010, which has Indonesia's Papua Province on the reverse side. This is probably the pick of the two.
Trekking maps If you’re planning on trekking, or just want more detailed maps, you’re advised to contact the National Mapping Bureau, order the maps you want and then collect them from the office in Port Moresby when you arrive. The topographic maps range in scale from 1:2000 through 1:50,000, 1:100,000 and 1:250,000. They have the whole country covered, though they’re often out of stock, out of paper or out of date.
Kokoda maps If you’re planning to walk the Kokoda Track, the NMB’s Longitudinal Cross Section of the Kokoda Trail (1998) is very useful, though not to scale. It’s available at the Kokoda Track Authority.