How do i get a european passport without a visa?

Your father was an Italian citizen at the time of your birth and you never renounced your right to Italian citizenship. Your mother was an Italian citizen at the time of your birth, you were born after January 1st, 1948 and you never renounced your right to Italian citizenship. Your mother was born in your native country, your maternal grandfather was an Italian citizen at the time of her birth, you were born after January 1, 1948 and neither you nor your mother ever renounced your right to Italian citizenship. Your paternal or maternal grandfather was born in your native country, your paternal great grandfather was an Italian citizen at the time of his birth, neither you nor your father nor your grandfather ever renounced your right to Italian citizenship Doesn't look like you able to get Italian citizenship

If your father did not denounce his Italian citizenship when he was naturalised in Australia, you are eligible for Italian citizenship. Contact the Italian embassy or consulate nearest you for the forms. Your father will need to supply a copy of his birth certificate and/or his old Italian passport, as well as a copy of your birth certificate.

It seems impossible because your father when he became Australian citizen, interrupted the line of continuity as Italian citizenship concerns. More likely your mom lost as well when she became adult because at that time she should have applied for reinstatement of citizenship. You should check also on the Australian end.