how can i stop my ex wife leaving tasmania australia with my son. is there a travel ban that can be put into p

I believe that there might be, but I am unaware of the exact law or government legislation to refer to, but at a guess try the following

write a love song and run through the air port and be like, I HAVE TO STOP THE WOMAN I LOVE FROM GETTING ON THAT PLANE!

and then sing it to her on top of the plane and have everyone looking at you and then tell her how much you love her and and say something like i wouldnt be able to go on without you!

and then happy indie music would play in the background and the cameras would spin and then the credis come

*applause*

Depends on the divorce decision of the court and its exact terms.If you have the right of access to your son,file a complain at the Director of Public Prosecutions, Office of the
Prosecutor on duty and show a prima facie case that your ex wife intends to flee with your son...good luck!