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SweetDee
Wilson
You could also check the basement of More's City. There is a place there that carries hard to find flours. Print or write this out and that should help you. I found some on-line from a Japanese site (usually deliver within three days), but it isn't cheap. 3 kg (3 x 1kg bags) runs around 7,500 yen.
ヴァローナココアパウダー or ヴァローナココオパウダー
I have a Chef friend in Tokyo I will be seeing this Saturday. I will ask him too...
Here is another location that sells it in 3kg or 200g packages. A 200g package is around 700 yen (I assume shipping would be an additional 300 yen. I know you said you don't want to order online, but these are online in Japan and deliver sometimes the next day, but never more than 3 days.
They also have a store inside the Sogo Department store at Yokohama Station. Maybe they carry some there...