There used to be a Tumblr blog called Sherlock Unravelled that would often find clothes and accessories worn by the actors in various episodes and post them. They were often quite expensive! It appears to no longer be on Tumblr, but it looks like they are on Instagram: www.instagram.com/sherlockunravelled Maybe if you look through there you can find it! Otherwise, perhaps Brooks Brothers might have something similar, based on my (admittedly not extensive) knowledge of men's fashion brands.