There are a few ways, some of which are...
1. Pay money to a service for the information (normally fairly reliable)
2. Use a free online search (can give interesting results sometimes)
3. Have friends in the TA/Airline industry (How many friend favours do you have?)
4. Call Qantas etc. and ask.
Some threads that might help:
http://www.frequentflyer.com.au/disc...pic.php?t=1163
http://www.frequentflyer.com.au/disc...pic.php?t=1209
http://www.frequentflyer.com.au/disc...pic.php?t=1732
[Note that KVS have changed their pricing and free access, so some of the information given about it may be out of date]