When the movie studios and TV shows are finished with their costumes, they don't stick them in storage. That would be too expensive. Instead, the wardrobe items worn by all those actors, actresses, and extras are sent to the vintage clothing market, where all those true designer garments are sold by the piece at a drastic discount.
It's a Wrap! is Hollywood's second-hand clothing store. Jason Cochran tried a little TV history on for size: