Firstly. the costs of recovering the debt – including the legal fees – are all payable by the non-paying owner so no need to worry about that.
The next step, if it hasn’t already happened, would be to place a caveat on the title of the unit so that if the owner sells, you get your money before he gets his.
I’m not sure if pursuing for bankruptcy is a good idea or not. Your legal advisers might tell you.
If your owners Corps is suffering financially as a result of this non-payment and you need the funds now, consider taking a strata loan out – the interest on that would be covered more or less by the penalty interest chargeable on the unpaid levies.