There will be more Serenity screenings on May 26.
Of course, the all-important question is where, and I don’t know yet. (‘nother update: there’s a screening in Dallas. Get those tickets fast; Seattle and Atlanta are already sold out.)
Note that the movie title is listed as “Special Advance Preview;” that’s what you need to search for, because it won’t say Serenity anywhere at all. (My ticket stub from last week says “Special Advance.”) So if you know of one of the theaters that showed the preview last time, go to Fandango, look up the theater, change the date to May 26, and see what’s showing at 10 p.m. Searching for “advance” might turn it up.
How to get tickets: keep an eye on the Browncoats forum thread (login req’d; it’s under Movie Production Related -> Crushing Disappointment) or the Can’t Stop the Signal site, which hasn’t been updated yet with the new showings but should be sooner or later.
Final update: all sold out.