Duncan's Toy Chest is not a real store; it was a made-up name for the movie "Home Alone 2: Lost in New York." The fictional toy store was named after the movie's executive producer, Duncan Henderson.
The inside of the toy store in the movie was modeled after the real New York toy store FAO Schwarz. The exterior of another store, the downtown Chicago, Illinois, store The Rookery, was used in the film as the exterior of Duncan's Toy Store.
According to IMDB, other than the toy store's exterior, the rest of the movie was filmed in Central Park at the Plaza.