If you bought it in the US, you're going to need a whole new transformer, unless the one you have can switch to 230-240V, which I doubt. You already know this Sorry if this sounds condescending, but don't use the US charger in Australia!! This will destroy your new toy.
The alternative is to take a photo of the specs listed on the transformer and post them in here. You can use www.bbpix.com or www.photobucket.com to host the pics for free or you can just post the specs - in particular the 'Output' specs.
No problem, mate, Tandys or •••• smith everywhere in Australia have all sorts of local trannies, and we are 240v 50hz, usually cost around 10-30 Aussie Dollars, although a lot of new systems have multi voltage trannies so check first