Are you rich and powerful? Because if so you could get one yes.

I couldnt get a gun. I couldn't just nip round my mates house and nick his dad's. They are rare and expensive and risky af to own. Not just anybody can have one. I bet most people in the West outside USA havent even seen one. You're not going to need one to defend yourself from one because the people who actually have them aren't going to risk getting caught for a simple mugging, and theyre not walking around constantly strapped in case they lose their temper at some mundane shit.

If you want a gun to protect yourself from guns, you're already living in Breaking Bad.

Edit to add : im not Australian but I assume its the same everywhere where the bad has worked