Wel come to YT
I'm sorry to hear your boy is suffering from bladder stones and a liver shunt.
I'm posting a link to another thread
Dr. Karen Tobias And Liver Shunt Repair
One idea I've had is if the specialist's in Australia aren't very knowledge about best treatment protocols, I believe that Dr.Tobias does do consults with vets.
Anyhow, look at this thread, post number 2, gives you a link to website on Dr.Tobias.