The most straightforward way to have this would be to have a new database table with the following fields: date, location, and hyperlink. A set of trusted users (including one or two from each regular group) could add, edit, or delete records. Periodically, records with dates more one day in the past will be automatically purged.

There's no need to automate this, since maintaining it takes a small amount of effort relative to the effort of organizing the meetup.