Hmmm I had this issue with mine, bought it from VIC, drove it up, they just needed the VIC rego papers and to see the VIN (physically, to match it up with the papers) and was good enough for me to get through first time NSW rego issues.
Anyone who needs, try this site http://www.complianceplates.com.au/ I emailed them with my VIN and some other details and they made me a new plate to replace the missing one for $80 delivered
I just went through the same thing recently. I took my '89 Z into a roadworthy centre in Victoria and they failed it because it didn't have a compliance plate but it had passed a previous roadworthy on this issue. They said it would be the first thing they would look at and it needed a compliance plate. After googling, I found this thread that brought up the 15 year rule which added a bit more to my confusing as I couldn't understand how the previous owner had registered the car when he had bought it. To clarify the issue I actually went into VicRoads were they explained to me that as long the car had a history of registration in Victoria then I didn't need a compliance plate. They even printed out a bunch of paperwork and a contact number that explained this and I took the paperwork back to the roadworthy centre and they passed the car. I had to make an appointment to register the car as I had handed in the original plates some 2 years earlier while I was rebuilding the car and it was off the road. In the end I didn't even need to present my car for any type of inspection and got my new plates on the spot.
