Perhaps look at what the Perth fans do and organise it like a meet? Spend the day together as a group with tables, trading and talking for as long or as little as you want. Even if you don't have much to sell, you'd only need to sell enough to cover as much or as little of the table fee you need to make the day worth it as a meet.
Or if you have two or three people here who intend to sell stuff, it can be a meet area for others to hang out (who are trusted enough to be around other people's property).
The regular meetings at the Parra and Nexus fairs draws in a growing number of people from here, because of the regularity of the fan-meet, like an annual convention.
Unfortunately Sandown doesn't appear to be within walking distance of any shopping centers (like Nexus & Parra fairs do) to meet up later as a group if you looked at doing the Parra Fair concept (arrive early as a group of non-sellers and fall back to a food court until midday-ish).
The good thing though, is it is next to a train station, so depending on how reliable the trains are to there, it makes for a convenient location.