I'm not Slim, but I can answer a part of your question. I hunted buffalo in the Northern Territory in 2000 using my .375 JDJ. The N.T. was the only Australian state still allowing the import of handguns for hunting, others having stopped it sometime prior. However, by the beginning of the following season, the N.T. also stopped allowing their import. It has never been resumed. I'm told that I was the last person to be able to there with my own handgun.
Some Australian outfitters are providing their own handguns to foreign hunters who want to use them in the N.T. and Arnhemland. The caliber of those handguns is .44 Mag. and perhaps larger, but that's all I know regarding the first part of your question.