Reading your question indicates to me a bit of a culture clash here - while I'm sure that Australian workplaces are not massively different from American (or any other), there is definitely some variation between cultures.
While this is skirting very close to legal advice, I'm fairly confident that in no workplace in Australia would you, making one HR complaint about a colleague or superior, end up with a lawsuit for harassment.
You might not even need to go to HR.
First, ask for a private meeting with your boss. Tell him that you are very uncomfortable with his joking about your accent. Say that while you know he's only messing about with it (even if you think otherwise - this is not the time to start making accusations), it is affecting you adversely and you would prefer him to stop it. You do have to allow for the fact that this person is simply obnoxious/ignorant rather than malicious.
Make a note of the meeting date.
Then, if he continues with the mocking, or starts some other form of bullying, make a note of what he did and when he did it, and who was around to witness it.
If, after a couple of weeks, he doesn't stop, talk to HR and mention that you have taken it up with the individual and he has continued despite this.
Hopefully, this will be the end of it all. However, if it doesn't stop, try HR one more time. If that fails, then I suggest you talk to your lawyer to get advice on the bullying, and start looking for better job.
However - if you have other reasons to think that this bullying won't stop (other people have been bullied) or he really will sue you for harassment (there's stories of him doing that before), then simply go straight to the end of this scenario and get a better job.