I found a very nice site for all UK based bakers who need baking equipment like diastatic malt powder etc.
I think this is a wonderful site
I have been looking for adequate substitutes for Granary, Hvedemel, and sigtemel for a long time. If anyone has one, please share it with me. Right now I try to combine flours and malt powder to make a granary flour, I use organic white wheat for the hvedemel, and I combine white and rye for the signtemel. Sigtemel is a very old grain combination in Denmark and we always made our morning rolls for it. I lost my source for supplies for these grains.
Maybe this won't help you very much in your quest for granary flour in Japan for granary flour is so unique to UK, I don't think you can find outside UK, but hopefully this info will help you to make your baking life in Japan better.
I'm sure you've noticed home-baking is extremely popular in Japan, there're number of very good suppliers of various kinds of flour, many of them imported from Europe and U.S.
These are two of the lartest ones with online shops. (I tried to hyperlink their URL but some of them triggered TFL's anti-spammer system, so please google them on internet yourself.
Cuoca (クオカ）ー They have 155 kinds of bread flours! They also have 3 shops in Tokyo, one is Takamatsu (H.O.) and also in Fukuoka.
Mamapan (ママパン）- Almost as many kinds of bread flours as Cuoca, too. Many of them are used by professionals.
There're many other very good online and actual shops for baking ingredients and equipments in Japan if you search on internet.
This is another one of the big names, but they only do equipments, not ingredients.
Majimaya（馬嶋屋菓子道具店）- they also have a shop in Tokyo
If you have any problem in deciphering Japanese on those sites, let me know. I can help you in that. .....and if you already know those places, sorry! :P