Trying to buy vegetable seeds and starting to grow your own food? Dream on, or try Tane no Mori ("Seed Forest") in Saitama. They have carefully selected the best organic seeds and heirloom varieties that are suitable for Japan's climate and soil. They aim for sustainable agricultural practices, without chemicals.
You can download their catalogue from their website or they will send it to you by mail.
Nothing beats the winter blues like reading a good seed catalogue, planning ahead!
Link: たねの森 (Japanese only, but most vegetables are written with hiragana or katakana)
Photo of Kami-kun and his wife Ai-chan from a nice article in Asahi Shimbun about their "blue-sky market" event in Koma, Saitama, called the smallest market in Japan.
If you live elsewhere, try Fork & Bottle for a good list of companies that sell organic, heritage seeds. The Kitasawa Seed Company in Oakland, CA has a large variety of Japanese seeds (but also some hybrids that I don't particularly like, because you can't save F1 seeds).
Kitasawa Seed Co. has been in the seed business since 1917, survived the WW2 Relocation Camps, and now has more than 250 varieties of traditional and heirloom seeds of Japan:
Kitazawa Seeds proudly continues to offer the highest quality Asian seeds to delight the diverse palates of our customers. We offer over 250 seed varieties that produce dento yasai or traditional heirloom vegetables of Japan, to the Asian vegetables popularly found in farmers' markets, specialty grocery stores and restaurants. Now you can grow them in your kitchen garden, sell them at your garden center and grow them commercially.