It's too late. The guns are already out there.
The only answer I can see is martial law, send the army to everyone's home and confiscate all the guns. But that's not an answer because there will still be a lot of guns hidden away. Or it will start a not-at-all-civil war.
And don't talk to me about Australia. That country was built on a prisoner culture, and their head of state is still the Queen of England. No wars were fought for them to gain their independence - since they are not really independent.