I bought this at a vegetarian shop in Kyoto (~15 minute-walk from Kyoto station).
I discovered this just recently because my husband tasted a takikomi gohan cooked by a friend who used this very product. My husband really loved that takikomi gohan so he bought this seasoning (which happens to be the smallest pack, 500g for ~￥750.oo) and kept on bugging me to replicate that dish. I'm not sure if I perfectly replicated it because the recipe I got from my friend didn't have any measurement (like most of my recipes here ^^;) but my husband loved it so much.
If you want to buy this or browse over other vegetarian products they sell at that store, you can check out the blog I wrote about them.
There are many kinds of mushroom powders. I've probably used 7 types in all. But as I have very limited stuff at hand, I will show you only two of those.
The one on the right is my husband's favorite.
It goes in an airtight plastic container and I know "Knorr" will come to your minds when you stare at the logo. I actually believe it is a product of Knorr but I'm not so sure. But if it is, it's probably good because it's an old, big and trusted company, isn't it?
The picture below it (lower right) is just the 500g version, twice the one in the bottle (250g).
This one below was a product I once bought from a Filipino friend who tried to start a business in the Philippines.
I like it very much because 1.) it's confirmed pure vegetarian; 2.) the product name "Shiitake Dashi" is written in Japanese 「しいたけだし」 ; and 3.) it's not wallet-painful, specially for starters because it was just Php80.oo per 60-gram pack.
If you want to check out these products and many other mushroom powders, here are links to the stores where these may be bought:
Wabi-Sabi Noodle House and Vegetarian Grocery | map | Facebook | blogger's photo of Wabi-Sabi's grocery rack
Happy Veggie Health Food | map | blogger's photos of Happy Veggie's grocery rack
Quan Yin Chay Vegetarian Food Garden | map | blogger's photos of Quan Yin Chay's grocery rack
If the above places are also inaccessible to you, you can check out the mushroom powders I saw sold online. I haven't bought from them, but I'll probably resort to them in the future. Check it out.
I was able to buy this one recently only at Quan Yin Chay Vegetarian Food Garden at Binondo, Manila. A 200g bottle is sold for Php 230.oo, I can't clearly remember. It started at Php 180.oo years and years ago but recently it looks like the supply's really getting small resulting in a sudden price increase.
I'm not sure how to read their company, but it goes something like: Taichu Jitsugyou Kabushiki Gaisha (大中実業株式会社). Their store is located near Kyoto Station, about 15-minute walk. I'm not sure but I think they ship products to other parts of Japan (you can call them to make sure). They have different products-- from frozen vegetarian products (like soy ham) to textured vegetable proteins (TVP), to vegetarian seasonings et cetera.
You can check out some of their products shown in the pictures below. But that's not all they have. I didn't have time when I went there but I really wanted to take pictures of their products for my blog (because they haven't created their website yet). Just click on the picture to see the whole photo.
If you want to buy or ask about their products, you can contact them at 075-671-6022 or fax at 075-671-4531.
If you want to go to their store, the address is written on the picture on the right. I'm sorry I can't translate it for you-- I don't understand it very well. ^^;