Australia doesn’t as a rule do a great autumn as the majority of our native trees are Eucalypts or Banksias which are designed to burn rather than lose their leaves. We do have some deciduous trees like the Flame Tree and the Silky Oak as detailed here
Generally our bush is a dull green with the occasional tree with lovely bark. So when the local residents have planted overseas deciduous trees in locations where there are very cold nights (most of Australia’s inland), the result can be spectacular. This spectacular is what I witnessed on my May day trip to Bundanoon, 2 hrs south of Sydney by car or nearly 3 hours on the slow train.
It is a really nice place to casually ride a bike as is nearby Bowral as described here >> and can Be found on a map here >>
See all the Photos in a folder here
So its read more about Bowral, Bundanoon and Mortan National Park here >> and find them on a map here >>

Other places down the Hume Highway
Canberra will be really good and Rosewood to Tumbarumba in purple here and the pick of leaves is Murray to Mountains especially Bright, Myrtleford and Beechworth
Another Autumn town is Mudgee near the Central West Cycling trail