If you want to listen to ham radio on your scanner, then try searching between these bands....
Amatuer radio contains a huge amount of radio spectrum that we can use ( I am a licensed amatuer ) and the only people that have more spectrum access then hams are the government and millitary. Amatuer radio bands are available to hams across all areas of the radio spectrum, from Low Wave to Microwave, so asking what frequencies are being used in Sydney is like asking where the needle in the hay stack is...
But the two bands I listed above are probably the two most popular around, excluding HF stuff. There are a stack of repeaters for the 2meter band (144-148Mhz) and the 70cm band (430-450Mhz) which are used for metro wide communications, and many are even linked to the internet and to other repeaters ( called IRLP ).
The Original Australian Scanning Site