I guess it all depends on where your interest in trains lies. If you're interested in local Australian prototype, unfortunately there isn't much available as far as train sets go.
Lima used to make train sets with reasonably accurate Aussie prototypes in HO scale (such as the Indian Pacific, the Overland, the XPT etc), but sadly they ended up folding a few years ago and were bought out by Hornby, who now market them as a sub-brand (and, as far as I know, no longer produce Australian-themed train sets).
Powerline used to also have some Aussie-themed train sets, also in HO, but they were really hard to find (I never saw them at any hobby shops here in Perth), and I'm pretty sure they've since phased them out in preference to single locos and rollingstock items.
I'm pretty sure nowadays the only prototypes available for train sets are either British (in OO scale), or US prototypes in HO (Lifelike does market some train sets as 'Australian', but they're really American prototypes such as the GP-38 and F-7 units repainted in Australian liveries which are perfectly fine for children or people who just want a nice looking train to run).
Finally, a good starting point bjay would be to pick up a copy of
Australian Model Railway Magazine the next time you're at a newsagent, as they have plenty of Australian hobby shops advertising in there which do mail order, which would be useful for you.
