I want to make a lemon tart, but I want tins with straight walls, like the ones in this image.
How would I find them - is there a name I can look for? I've been unable to find them online (and they need to be shippable to Australia).
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.