Congratulations on your new aquisitions!
PTS are found on Bougainville and Buka, as you mentioned and have also been found on the islands of San Cristobal, Makira, the Shortlands, Choisel, Vella Lavella, New Georgia, Isabel, Guadalcanal, Ngela, Malaita, Ugi, and Santa Ana. All of these islands are part of the Solomons Island archipelago. The first are part of the country of Papua New Guinea, the rest make up the bulk of the country of The Solomon Islands.
Skinks have been found on all of the islands listed above, but many of those records are old (30s, 40s and 50s) and a lot of logging, mining and other development has taken place in recent years, so they may not still occur on all of those islands. They may also occur on other islands that haven't been reported.
I too have been looking around to see who's breeding PTS currently. Rico and Darlene Walder of Signal Herps, who post here occasionally, breed them and according to his website, Raymond Goushaw of Herp Breeding Research. Those are the only commercial breeders I've found on the web. I know there are plenty of private individuals out there breeding though. There are also a few places like Walkabout Farms and the Tewksbury Institute of Herpetology that have breeding/research programs ongoing for PTS.
Who did you get your 4 from, if you don't mind me asking?