You can sell them on Ebay too. You're in Victoria and there are heaps of pet shops there and most of them will buy fish from customers. If you get too many for the shops to take and you have thousands of healthy nice looking fish, you can contact the major suppliers in Australia.
I'm pretty sure Aquarium Industries is in Melbourne. https://www.aquariumindustries.com.au/ They are an importer but sometimes take fish from local breeders. However, the fish have to be good quality and you don't get as much for them because you sell them bulk. But it can help you unload a few thousand fish if you need to.
I'm pretty sure Aquarium Industries is in Melbourne. https://www.aquariumindustries.com.au/ They are an importer but sometimes take fish from local breeders. However, the fish have to be good quality and you don't get as much for them because you sell them bulk. But it can help you unload a few thousand fish if you need to.