This was one of the best places to buy Copic markers (and lots of other supplies) in Tokyo. Don't confuse the Itoya art supply store with the big Itoya stationary store next to Tiffany's on the Main Street. It is a short walk from the Ginza station in the alley behind the big flashy Itoya stationary store. Happy shopping!
I have this app, it works great gives suggestions and lets you put in what style you have incase you like me started with the original and are changing over, plus you have it when your at the store too. great app!