If I buy something from a company over ebay can I still sue if it never turns up? (Australia)

If there is a registered office in Australia, you will most likely be able to claim against the company by lodging a claim in the amll claims tribunal or the local court. In queensland, matters regarding a debt of less than $7500 are heard in this court. You would need to conduct a company search to find out more about the company with ASIC before proceedings, and so that you can draft the court documents correctly. However, I believe that you would have a good chance of succeeding with a claim like this as long as you can document all of the appropriate things which you need.