Across America and around the world, people wander through flea markets to search for lost treasures. For decades, no such market was more renowned than the legendary Chelsea flea market, which sprawled over several blocks and within an old garage on the west side of Manhattan. Visitors would trawl through booths crammed with vintage dresses, rare books, ancient swords, glass eyeballs, Afghan rugs, West African fetish dolls, Old Master paintings,...