Dont worry about mains voltage in Sydney, in most places its spot on.
300 mA is about 5 times more than you need, even for both channels!!
A transformer giving 100 mA at 500 to 530 volts UNLOADED will be perfect for both channels.
A, 370DAX Hammond is exactly what you need.
http://www.hammondmfg.com/pdf/EDB370DAX.pdf
You might direct a question to, Ed Dinning for furher advice, OR criticism of my choice.
Joe