A simple google search learns me that 'tetroxin' might be the T3 brand available in Australia. might be something to check into further.
Before starting T3 I would ask to have your FT4 checked and increase the dosage though. If you're not having conversion issues, it's possible T4 might bring you where you need to be. It's easier to build up with T4 and when FT3 remains low or proportionally too low, add a bit T3 to the mix.