A Narrow Gauge Convention is always a good weekend...but I might be a bit biased
I will also be attending and driving up from Geelong. There are a number of B&B options around the general area, but nothing really within an easy walk to the venue. I will be camping at the nearby Moss Vale caravan park as a budget option (about 10km from the venue as a short drive). There are similar style accommodation in nearby Burradoo. Mittagong is also reasonably close by for other options. Which ever direction you head either side of the venue, there will be a mixture of suitable options within a 15km radius of the convention.
Hope you can make it down, as there is normally plenty to see, hear, learn and buy.