I'm in Brisbane ... and yes, there are a lot of bike riders here. However, Brisbane is about 50km from Amberley. Ipswich is much closer to Amberley about 10km.

For Brisbane: http://www.planetcycles.com.au/info/BunchRides.htm
For Ipswich: http://www.ipswichcyclingclub.org.au/ICC/Home.html (couple of rides listed at the bottom of the page.)

Also worth taking a look at http://www.roadgrime.com.au/ and maybe asking on the forum there.
The local bike shop might be worth an email as well: http://www.yellowjersey.com.au/

Hope you enjoy your stay