Yes, both the Ally and the Go are sold in Australia. However it's also quite easy to order a "grey import" Steam Deck from Amazon, which is what I did. I'm guessing the sheer number of Steam Decks that have been sold into Australia that way are factoring into Valve's decision, because anecdotally among my peers the Steam Decks owned outnumber the Allys 4:1. Pretty impressive for a device not officially sold here.
That'll probably be the big news from all this, further global release. I'm not holding my breath for the next iteration until the end of the next console generation (the upcoming "switch 2"generation)