I don't see any places online that sell those seeds in bulk. Apparently they have fields of it growing in Japan, but they aren't selling them. Why do you want to grow a lot of it? For the grain and health benefits, or for the red flowers? I think 1 plant can produce many seeds, so if you can't find seeds in bulk, after a year or two you should have enough seeds to fill a larger area, if they grow well for you.