I had made an inquiry to a tofu maker located in Katsushika Ward, Tokyo, who kindly gave me a reply the other day.
He dared not speak of how to make yose-dofu, because he says, "There are a variety of ideas of yose (literally, "bringing together") and "It will take a very long time to give you an accurate answer."
Instead, he recommended Mame Hyaku (豆100) of Taishi (タイシ)
http://www.taishi-food.co.jp/
He says, "It tastes fairly good for a big company" and "I once tried it, and it gathered together well (turned into good yose-dofu)."
I accessed the site and found the product very good and impressive. So, I'd like to recommend it here although I have never tasted it before.
One bottle of Mame Hyaku contains 500 ml of soy milk, and comes with a pack of 6-ml nigari, which is enough to turn the soy milk into tofu. A 350-ml bottle is also available, but does not come with a nigari pack.
A box of six 500-ml bottles costs 2,100 yen including the shipping charge and the consumption tax.
But even more impressive are the various soy products produced by that tofu maker himself. His name is Hiroyuki Arai (新井弘幸), coincidentally the same last name as mine (same Chinese characters too). His store, Saitamaya (埼玉屋), is located in Katsushika Ward (葛飾区) in Tokyo.
http://saitamaya.net
If you read this site, I'm sure you will find him a very interesting and diligent man.
I guess most of you don't read Japanese, so here I post an English article of a Toyota magazine covering Saitamaya:
http://saitamaya.net/toyotaindex1.htm
(Click on the photo of the article, and a larger photo appears. Click on the icon that appears at the lower right corner, and the photo will get even larger.)
The next time I visit Tokyo, I really would like to go to his store.
お返事ありがとうございました、新井さん。いつか、お店に寄りたいと思います。
Thank you very much, Arai-san, for your reply. I'd like to drop by your store some day.
***
Additional information (which I learned from a reply from Taishi):
This soy milk product, Mame Hyaku, is a "whole" type (ingredients not conditioned) and pure and, therefore, it expires in eight (8) days. When delivered to you by Cool Takkyubin (truck service whereby the goods are delivered either refrigerated or frozen), the product is already two days past the date of manufacture and is suitable for drinking within five (5) days only.