Josiah here, from HKCommons/SCC. StartupsHK indeed has a centralized calendar, it's an embedded version of the one centrally hosted on the SCC website -
http://www.smecc.hk/v2/calendar/action:month/ . It's based on a wordpress plugin but easily interfaceable with Google Calendar.
There's a lot of general SME events on it too, not just techy startup events (and not all are in English), so your mileage may vary, but it's something we've been working together on. If your organization wants a login to post events (there's a brief review process before publication, just to make sure there's no spam or anything), drop me a line and we can set it up for you.
Fully agree on the sentiment that the startup community though is worth consolidating - there's quite a few spheres that everyone seems to be a part of, though not necessarily overlapping.
Cheers,