Thanks to the other Jo who replied to the question about Yass, and to TOF who asked around at work.
We have two options. One is the site of an old garage which is still going (thanks Jo) and the other is, according to a colleague of TOF's, it is known as Ross's Relics (that is what everybody in the town knows it as, the business name may be something else).
It is located just before the Courthouse on the main street Yass.
Google maps here. http://maps.google.com.au/maps?f=q&source=s_q&hl=en&geocode=&q=Yass,+New+South+Wales&aq=0&sll=-25.335448,135.745076&sspn=37.134781,56.162109&ie=UTF8&hq=&hnear=Yass+New+South+Wales&ll=-34.841095,148.91033&spn=0,0.001714&t=h&z=19&layer=c&cbll=-34.841095,148.91033&panoid=gk5TX8LRN5dsXU4A1CRsDg&cbp=12,242.64,,0,3.87