If you are not going to eat it all, just use half of the ingredients. This is enough to fill out a big mason jar. Most supermarkets sell the below listed ingredients nowadays, you can find it with the 'exotic' ingredients such as sushi rice and wasabi. The miso paste is the only ingredient you have to buy in a specialized shop (bio or Asian foodstore) but you can keep if for a long time in the fridge and you can use it to give some extra taste to soups, sweet potato puree or to make the famous miso glazed black cod. A lot of options.