I've been using one since the early 1990's. I was playing 2e back then and found that a Battlemat just made things easier, both as an explanation tool for the DM and a visual aid for the players.
In 3e, I find that a battlemat is almost essential to run combats smoothly. Just dealing with attacks of opportunity makes the mat worthwile.
As for getting one, I bought my first mat from Chessex. It is a Megamat with 21mm squares. Back then, that was the scale of most of my miniatures and the ones I was buying. Now the scale has moved up to 25mm. Therefore, if you get one, make sure to get the 1 inch squares one.
As for getting one in Australia, being from Canada, I can't help you there. I have dealt with a few online ordering business. You might have some luck there.
Guillaume