You know how small towns love to hold an annual festival centered around a unique theme? Near where I live, there's the Daniel Boone Festival, because he came through the mountains there, and the Chicken Festival, centered around the home of Kentucky Fried Chicken. There are a lot of places where their biggest claim to fame is that a movie was filmed there. If it was a popular movie, the festival can draw a substantial crowd of fans from far away.
Blobfest is a bona fide vintage film festival, although that one movie is shown every year. Read about quite a few other fan festivals based on movies you can attend across America and elsewhere, at Cracked.