Would you use a site that's free to post job for transport needs?
Car carrier, store deliveries, freight... *if so, what would you use it for and how often do you think you would use and what location (just suburb and state)?
Your question is a bit vague, so forgive me if I have got it wrong, but it sounds like you are thinking about running a courier service for larger objects? If you are just starting out, you could try Gumtree and Craigslist to get you started. Depending on what areas you plan to cover, you could try advertising in all states, suburbs and towns in that area with a view to picking up backloads.
As you start to get some business though, I would strongly recommend setting up your own website so that you look more professional, then start marketing your business through social media, both free and paid ads. Hope that helps, but if I have got it wrong, just let me know with a bit more detail.