How do I find tart pans like these?
First, those are not a "tin" which may explain why you've had trouble finding them. They are individual tart rings which must be placed on a baking sheet. Sometimes they're called flan rings or, if they're larger, cake rings. 

If you do a Google search with Australia "tart ring" you'll see that plenty of baking supply businesses in AU sell them.  

Good luck!