Hey there Katarina. I know that marijuana-seeds.nl ship to Australia and they get through customs like 99% of the times. There stealth shipping option is very good. I'm based in the US and have used them a few time, but have spoken to growers on here and on the other forums in Australia who have got great things to say about them.
I'm not familiar with any Australian based seedbanks, you could probably get some from Nimbin if you popped up there!