IF the map shown is generally accurate as to location, then this is in/on private property in Bon Air. Without someone RSVPing, actually registering, the exact location will not be known. Willing to bet that one must be on an approved list. If on the off chance the don't control by invitation only who attends, carrying or challenging their rhetoric will get you an invite to leave.....and this looks to be on private property.
Then to register, I would want to use a throw away phone and special email account to keep from contaminating those I use now. Over all I see MDA as extremely small, even tiny, and ineffectual. A number of us attended a rally they held in a public park some years past. They had a dismal turnout. Nevertheless, if anyone finds out anything different, I would be interested to know about it and I believe it is good to have an undercover agent on the inside of such groups - always potential for valuable intel.
Please don't take this as a totally negative response, just don't see that a sizable group is needed. One or two is the magic number to see this from the inside.