Midoriya is a Japanese mini-mart in Williamsburg, Brooklyn. They sell all kinds of Japanese foodstuffs, kitchen items, and other miscellaneous useful things.
It is clean, bright, and cheerful—one of the tidiest little stores I have ever seen in New York City. You can go there for your lotus root, quail egg, and rice ladle needs.
There are a lot of packaged and canned foods. I tend to go for fresh stuff, so it is not so much my scene, but it would be a great destination for people with particular Japanese food needs.
And there were Japanese-speaking employees when I was there, so you can probably try out some Japanese, too, if you like.
167 North 9th Street
(between Driggs and Bedford avenues)
Brooklyn, NY 11211