Could you be able to create a system where all cellphones of dollars member all over the world could ring together like in anime?! I post that YouTube video I found to give you an example!! Don't pay attention to the fact that this is only during an anime expo please! It would be just TOTALLY really wonderful if all members could be called if it's necessary like in the anime!
Unless we got another Durarara adaptation, which results in a sudden popularity of Dollars, a large scale meetup is unlikely. But if you're willing to do the 'homework' and are determined, slowly and steadily gather members of Dollars in your local area is a viable option.