Dedicated style hounds are honing their hunter-gatherer skills by tracking down secret addresses known only by word of mouth. Five of our favorite private shops: LONDON: Ring the doorbell at Saturday (26 Chilworth St.; 44-207/706-7271; open Saturdays only) to enter an ornate Victorian space where England's edgiest fashion labels are displayed on industrial racks. MILAN: Sporty types hunt down Diesel's infamous streetwear at 55DSL (75 Corso di Porta Ticinese; 39-02/8324-1649), an apartment-style boutique in an inner courtyard, complete with a 1950's fridge and showers. ROME: People often mistake Pozzi Lei (8 Via Roma, Treviglio; 39-0363/46383) for an art gallery—it sells unusual pieces by Stella McCartney and Miu Miu, along with sculptures by architect Vincenzo De Cotiis. NEW YORK: Hidden down a long hall, the windowless Alife Rivington Club (158 Rivington St.; 212/375-8128) stocks retro and limited-edition sneakers. BUENOS AIRES: You'll need an appointment to stop by Arte Etnico Argentino (4656 El Salvador; 54-11/4832-0516), where Ricardo Paz showcases handwoven rugs as well as antique furniture carved from carob trees.