Items listed on EBay Australia does show up on a direct search when on the US Site. As Chadjaja noted, you do have to allow international shipping. On the search it will come up in AUD, but will also have a conversion into USD.
You can list on the US site, as you will get a larger audience, but you have to remember that the sale price is in USD, so it may be unreasonable for you to ask for payment in AUD.
Many buyers in US though are a bit weary of Non-American seller, and the bidding will be a bit lower than if the item was in US/Canada.
That said, I would recmooned selling big items on EBay USA.
Ersk