Atishoo, may I ask when you looking to travel? Gulf Air got great specials from London to Aus, but within a spesific time period. Its a good airline, but then you have to take a connection flight via Bahrain though..
I dont know about any airlines that provide free internal flights, but if you are sure about your dates, you can pick up internal tickets for really cheap. (usually these tickets cannot be changed after you purchased it) Where do you want to go in Australia?