While the start of May ushers in a flurry of fairs, auctions, and exhibitions in New York City, there’s nothing quite like Collective Design. Launched three years ago by the architect/interior designer Steven Learner, the fair is dedicated solely to collectible design, including furniture, jewelry, and decorative objects. But Learner wants visitors to do more than buy at Collective Design—his goal is for the fair to serve as a conduit for education, exploration, and discovery.