This is the combined group LucasFilm approved Star Wars Costuming Clubs. Including 501st Legion, Rebel Legion, Southern R2 Builders, Saber Guild, Dark Empire and the Mandalorian Mercs.
501st, Rebel Legion, Mandalorian Mercs & Saber Guild
The 501st Legion is an international fan-based organization dedicated to the construction and wearing of screen-accurate replicas of Imperial Stormtrooper armor, Sith Lords, Clone Troopers, bounty hunters, and other villains from the Star Wars universe. The 501st Legion, called by its nickname Vader's Fist, is made up entirely of volunteers.
Formed in South Carolina by residents Albin Johnson and Tom Crews in August 1997, the Legion now has over 14,000 active members worldwide, with over 26,000 approved costumes. The Legion is active on 6 continents, with local units known as Garrisons and Outposts in over 60 countries. Legion members make appearances at casual, promotional, and charitable events, often at the request of Lucasfilm's Fan Events department. Although not officially affiliated with the Walt Disney Company or Lucasfilm LLC., the 501st Legion is Lucasfilm's preferred Imperial costuming organization, and its members were featured as extras in the official series