We might be able to rig up a member map but it would be using a google map and so the info would be public. Would you have concerns about this?
Another option might be a rally / event calendar function but it would not work well with mobile devices. Here's an example of one at another forum. If you click on the event, you see options to rsvp to attend. Airstream Forums - Calendar
(note that if you are not logged in you will be asked to join the mailing list - just dismiss that).
Here is a third option - this is a rally map for another forum that is actually maintained by a member. As a google map it must be controlled by one or two individuals who enter all data. We could use something like this and then link to a discussion about the event in the description. https://www.google.com/maps/d/viewer...Y.kH9EkyWon6YM