Introduced in『JAPAN : THE VEGETARIAN COOKBOOK』by Nancy Singleton Hachisu

Koji & Co is listed in the resources in Australia in
'JAPAN : THE VEGETARIAN COOKBOOK'
by the author Nancy Singleton Hachisu (2023)

Nancy Singleton Hachisu san, the author of cookbooks:
Japanese Farm Food (2012),
Preserving the Japanese Way, (2015),
Japan: The Cookbook (2018), 
Food Artisans of Japan (2019)

In around 2020, when Saeko was trying to find information sources about wooden Kioke in English, she came across Nancy san's writing in an article :

Less than 100 years ago, all Japan’s fermented products — including soy sauce, miso, mirin (sweet cooking sake), rice vinegar, sake and pickles — were made in wooden barrels. There is a good reason for this: Fermentation relies on a healthy environment where microbes can thrive, where enzymes and yeasts can work in symbiosis. Kioke are the ideal vessels for this because the wood itself is host to millions of beneficial microbes. Some maintain that the kioke is more than just a tool, it’s the essential ingredient required to authentically ferment Japanese foods.