Caravans not sure if they have trailers though?
187 Hastings River Drive, Port Macquarie - Phone: 6583 8870
These guys hire but may sell used ones:http://www.habitatcampers.com.au/trailers.htm
Heres one on the Nth Coast:
NORTH COAST & QLD Woolgoolga (NSW)
Rob or Sue (02) 6654 7014 or 0413 310 876
Heres some private sales:http://www.exploroz.com/Trader/Campers_Trailers.aspx