Etro is not a widely available brand in London. Liberty usually has a decent selection, and currently Fenwick, just up the road, is featuring the brand. The only other way to get hold of Etro scents is to visit the Etro shop, just off Piccadilly.
It’s quite an easy shop to miss; the name is visible only on the canopy, which cleverly hides the shop name stencilled on the window. You’re also likely to be dazed by the profusion of designer goodies on either side, including Bottega Veneta next door…