Bike Hour? Every equinox?
Why limit yourself to that. There is a 'bike hour' every month, in accessible urban locations. They even have one in Tasmania. If it's not accessible start your own. Known by the slight double-meaning of 'Critical Mass', last Friday of every month, at 5.30pm in most cities.
BTW, advocacy groups don't want to have any connections to it, and I see why and understand it. CM operates as a 'disorganisation'. Any links with formal organisations lays them open to charges of running a 'march' without a permit - shades of Bjelke's anti-march control mechanisms .