Roy, the type of wagon you're looking for is called a shunter's float. I'm not sure if there is a NSWGR one available but I definitely know there is a Western Australian one on the DLS (WAGR NS class) made by John_SB - only issue is it's in Westrail colours naturally and has a tool chest in the centre, plus smaller handrails. And despite it's prototype being narrow gauge the Trainz version is standard gauge, so it would at least work as a stand-in for you for now if you're really desperate. This is the KUID: kuid2:60318:1143:1 (I think there is a later version for download to the one I have installed).