I'd love to start selling cupcakes at markets, but I'm in Australia, and it can get VERY hot in Summer. How could I keep Buttercream or ganche fresh?

I have done farmers market this year in 90 + degrees, and do face the same problem. My problem though is not so much heat, as direct sun. If the sun hit those cupcakes, it "goodbye frosting" This has been an issue and some have addressed it on other topics, but I can't find them right now, maybe you can do a search. I have heavy plastic containers, and I set my cupcake containers on ice packs. It helps. I also have heard that some put only a few out for display, keep the rest in a cooler and trade them out when the ones on display get too warm.
Sorry I can't help too much. Hope this gives you some ideas