Fathers permission to enter Australia

Hi am looking to come to oz intially for holiday and hopefully long term to settle, have two children from previous relationship who have no contact with their father have been told that I have to show every effort made to obtain permission but as have no idea of wherabouts is impossible,

visa office say visa will most likely be granted if provide written declaration of circumstances and evidence have made efforts to get permission but that at border will be stopped and grilled again and is discretionary if will be let in

Does anyone have any knowledge or experience on this situation? obv dont wanna spend fortune on booking hol to be refused entry at border.

Have spoken to uk solicitor and they say will be unable to apply to court for residence order as no dispute over residence