There is Reebonz who sell preloved designer goods online and they also have a store in Sydney CBD. I've also seen online australian sites like mynetsale.com.au sell preloved LV sometimes (but not always).
I find buying from trusted Japanese eBay sellers the way to go to buy preloved LV. The supply of preloved LV there is huge (not to mention the quality much better) so the prices aren't as steep as you would have to pay domestically. You can also often find that some sellers have free express shipping - I just recently purchased a preloved LV speedy 30 in epi fawn which took 4 days to arrive from Japan!
I find buying from trusted Japanese eBay sellers the way to go to buy preloved LV. The supply of preloved LV there is huge (not to mention the quality much better) so the prices aren't as steep as you would have to pay domestically. You can also often find that some sellers have free express shipping - I just recently purchased a preloved LV speedy 30 in epi fawn which took 4 days to arrive from Japan!