Loloata is ok, but as an alternative, you can also dive from Port Moresby's Bootless Bay via the Dive Centre. John runs a nice operation with great freedom for photographers. He knows a plane wreck which is great for wide angle (visibility permitted). I have fond memories of Horseshoe Reef and Suzies Bommie as dive sites. Make sure you have a safety sausage or even rent John's dive reel/buoy if you go to the bommies on your own, it's a long way back if the boat loses you to the currents!
Depending on where you are going with your holiday, there's also Madang, Tufi, Kavieng, Rabaul among other towns with diving and resorts as well. You don't say so it's hard to give you the right info.