Where can I buy onsen powder in Tokyo?

some shop ( name and if possible adress) in Tokyo where I can buy onsen power for a tub at home. And with a large selection of product please.

Thank you

Tokyu Hands has quite a large selection.

I researched and found that Tokyu hands has many stores but I�Lm really interested in the Shibuya branche because it�Ls really big. Is the branche near Tokyo Station also as large as in Shibuya?

The one adjacent the station in Daimaru? No it's relatively small, sharing half of just 3 (or 4?) floors in the Daimaru department store.

The Shibuya one is good, but I tend to prefer the one in Shinjuku Times Square because it's better located for where I like to shop.

is there a Shop near Akihabara? Other than in Tokyo station.

I just go to a reasonable large pharmacy/drugstore in whatever suburb I'm shopping in, and I always find a good selection, different colours, perfumes, natural or not, whatever takes my fancy. Never been hard to get.

Don Quixote in Okachimachi should have them.
http://www.donki.com/en/store/shop_detail.php?shop_id=107

Yodobashi in Akiba I think has also started selling "drugstore" products (Bic in Yurakucho certainly has).

Go to Don-ki (nick of Don Quijote : ƒhƒ“�EƒLƒz�[ƒe(Don kihoute)/store name).
http://www.donki.com/en/store/shop_detail.php?add=1&shop_id=98&pref=13...
http://www.donki.com/en/
onsen powder/bath solt : “ü—��Ü/nyuu-yoku-zai
onsen is ‰·�ò�@(“’�Fyu means hot water)
https://youtu.be/_lwRey2YpJQ

Now no 100Yen shop("Daiso" and more) in Akihabara but if in another area find easy and cheapest.

Sales ranking (include regular type)
http://www.cosme.net/item/item_id/1053/ranking
http://ranking.rakuten.co.jp/weekly/205761/
http://www.amazon.co.jp/gp/bestsellers/hpc/169649011
http://www.cosme.com/products/ranking.php?category_id=104
Onsen type package like this.
http://urx2.nu/qgUy
http://urx2.nu/qgUA

BTW, do you know your country water quality?
http://image.slidesharecdn.com/beeringredients-140116015525-phpapp02/9...
Austria is HARD-water but Japan is SOFT-water.
So "�d’YŽ_(Juu-tansan/Sodium_bicarbonate)/baking soda(�d‘‚/jyuu-sou)" type is better.
https://en.wikipedia.org/wiki/Sodium_bicarbonate
http://image.rakuten.co.jp/r-otasuke/cabinet/cabinet4/1097349_01.jpg
Basically only by (pure)baking soda mixed make chage to soft-water easiest.

Thank you very much for your detailed answer :) I didn�Lt know that there are different type of water for me. It help me very much.

Although I'm not certain if they have a large selection, Oedo Onsen in Tokyo sell their own.