Reading your post again - we are not looking for a closed forum, but rather a separate forum.
In the main overview of forums, I suggest a section called "Regional Forums". Under that, Hong Kong - and many other areas - as required. Could even be with subsections like Australia: Sydney, Melbourne etc. (depending on how much activity there is)
Many other larger forums of other interests has such regional sections. For cruising/boating, each member could then focus on those local issues like where to find parts and services, slips/moorings available, how to get a local license and so on.
We are also looking at a Wiki (for sharing places to anchor/fish/dive/swim etc, but also information about regulations related to getting a local sailing license), and looking at your cruiserswiki.org - except that one seems like it's not active?
I am happy to volunteer as moderator/editor for both forum and wiki if needed. But we need to establish first if it will be here - or another forum.