To bring your Thompson handguns to Australia, you will need a Handgun licence. To obtain this you will need to join a suitable handgun target shooting club. Get the licence, probably will need to attend a few course/education sessions, a safety practical test, and a written exam. Then possibly wait for X months before you can obtain your first handgun.

That is how it is for locals anyway. But check Victoria's own requirements. And maybe scout out suitable clubs and ask them.

If you have a number of Thompson handguns and want them all, check specifically if that will work or not.