I remember vaguely reading about buying fabric in Nippori near Tokyo where there are countless choices from HK U Travel magazine. Check out
Sweet Little Treat and
Floating World's visit to Nippori.
Ayumills listed some interesting links from her visit. Japan Jenny has a picture of a Nippori fabric shop
here. TripAdvisor even has a
How to go to Nippori topic.
Experience of two gaijins in Tokyo and Nippori, funny and entertaining. A Dress A Day had a
great time fabric shopping at Nippori for her amazing love of dresses.