New shops open here on a weekly basis, but it’s the rare retailer that can whip New York’s fashion seekers into a frothing-at-the-mouth frenzy. (Last year’s Topshop opening comes to mind.) Now it’s Isabel Marant’s turn. The Frenchwoman’s first U.S. store (469 Broome St., at Greene St.; 212-219-2284), which opened in Soho on Friday, finally makes the designer’s easy-to-wear, hard-to-find, slouchy-cool clothes and accessories permanently available. Here, fringed camo boots ($1,160) on the store’s ash-timber floor.