How to get Australian Transit Visa

The Transit visa (subclass 771) lets you transit through Australia for no longer than 72 hours if you need to pass through Australia on your way to another country

Check list -
 http://www.srilanka.embassy.gov.au/files/clmb/Checklist%20771%20-%20Sri%20Lanka%2010.07.2013.pdf

Application form -
http://www.immi.gov.au/Visas/Pages/771.aspx

Warning to people who choose Cathay Pacific airline to travel to New Zealand

Cathay Pacific airline does not have direct flights to New Zealand. There for passengers do have to transit either Melbourne, Brisbane or Hong Kong. You MUST HAVE Australian transit visa to transit via Melbourne or Brisbane. and if your transit hours are exceeding more than 12 hours you MUST HAVE Hong Kong transit visa. To get Australian transit visa it takes 3 weeks.  

Cathay Pacific Srilankan office will not give you these information until you purchase the tickets. May be not until you inquire. This might due to novice ticketing officers or purposely. Be aware.