Nintendo Handheld Console - New Nintendo 2DS XL - Black and Lime Green - Pre-installed with Mario Kart 7 (Nintendo 3DS) https://www.amazon.co.uk/dp/B07D88MXWH/ref=cm_sw_r_cp_tai_IqAhFb2523X0S
There are 700+ listings on ebay.
Amazon Aus has a UK listing that will ship to Aus.
These can be found anywhere you would otherwise find used games or used consoles. That said as these rely on secondhand market sellers, you can only find them when a store has inventory or when a seller makes a posting. I'm sure Aus has used game stores and buy/sell apps like most of the world does and there probably are many in Aus that have or will have a 3ds system in stock at some point.