Interesting, this case does indeed look to be a new variant - something in between the original 64 and the 64c.
I would say (without knowing for sure) that the original was surely released in Australia as well. The original C 64 was definitely released in New Zealand (I owned one), and I cannot imagine Commodore releasing in NZ only and not Australia given the 4-5x population advantage Australia has.
For what it's worth, here's one of the Australian C64 commercials of the era, clearly featuring the C64C. The original C64 breadbins were also very common in Australia:
The guy in that ad (John Laws) was a very famous talkback radio personality at the time - nowadays he'd probably be likened to a Fox News personality like Tucker Carlson. He was featured on the packaging art for the Australian C64 Family Pack, as seen near the end of the commercial. He was known to begin every episode of his radio show with the phrase "Hello World".
Note that Commodore bundled the Family Pack with a random book (mostly pictures?) about Australia. For some inexplicable reason there are an awful lot of secondhand copies of that Presenting Australia book available on eBay to this day.
Never seen one of these Slimline C64 Replacement Cases before. Intriguing!
If it has the heavy power-supply, consider replacing or repairing it. It fails over time by increasing the 5V rail until some chip or other fries in the C64.
It is an original C64 but a company in Australian made an after market case for it to make it look more like the C64C without having to buy an entirely new computer.
Note that he mentions the case is aftermarket (from Micro Accessories). I suppose the original case was just thrown out, which kind of makes me want to cry.
I would say (without knowing for sure) that the original was surely released in Australia as well. The original C 64 was definitely released in New Zealand (I owned one), and I cannot imagine Commodore releasing in NZ only and not Australia given the 4-5x population advantage Australia has.