Where to find Organic Nutrients for +3 Kindness
It's actually not called Organic Nutrients in English, it's called Mega Nutrients. It is also not in Shibuya, but in Shinjuku. From this GameFAQs thread:
It's called Mega instead of Organic in English and it's in Shinjuku, not Shibuya (in case anyone searches)
You buy them in the Flower Shop in the Red Light District in Shinjuku, not the underground mall.