Ocharaka in Nihonbashi has great selection of tea.
Other places are listed here:
There's a Japanese tea shop called ”Ippodo” in Tokyo, which is 5 min. walk from Yurakucyo Sta. (http://www.ippodo-tea.co.jp/shop/marunouchi-tokyo.html). They have various kinds of tea and you can taste them. They also have tea salon connected.