PARIS-BASED vintage dealer Gauthier Borsarello is the man clothing designers often go to when they want to buy a weathered pair of Woodstock-era Levi’s or a just-so military jacket to stir their inspirational juices. So when Mr. Borsarello, who formerly worked for Ralph Lauren, extols the virtues of the humble chambray shirt, it’s wise to listen carefully: “To me chambray is the best compromise in terms of density, breathability and strength,” he said of the way the fabric marries the ruggedness of denim with the dressiness...