I tried to go through the Certificate of Validation process a few years ago, but gave up with the bureaucracy. Part of the problem for me was that I was there over New Year, so the CASA office was not fully staffed.
I flew with Basair at Bankstown (Sydney), but would not recommend them. They were disorganised and the aircraft (a TB10) was poorly maintained.
More info from CASA
here, including how to obtain the required 'Aviation Reference Number' (ARN).