Are they just not uploaded anywhere or are there private trackers/secret sites I don't know about, anons?

e.g. マンガストーリー&キャラ創作入門
https://bookwalker.jp/de897c6191-a1c6-49c3-a8fa-44e2696719e9/
Not on https://annas-archive.org/search?index=&page=1&q=%E3%83%9E%E3%83%B3%E3%82%AC%E3%82%B9%E3%83%88%E3%83%BC%E3%83%AA%E3%83%BC%EF%BC%86%E3%82%AD%E3%83%A3%E3%83%A9%E5%89%B5%E4%BD%9C%E5%85%A5%E9%96%80&display=&sort=

e.g. 小池一夫のキャラクター創造論
https://bookwalker.jp/de42cdee1c-eb17-43c1-bf5d-0c3faa6be310/
Not on https://annas-archive.org/search?index=&page=1&q=%E5%B0%8F%E6%B1%A0%E4%B8%80%E5%A4%AB%E3%81%AE%E3%82%AD%E3%83%A3%E3%83%A9%E3%82%AF%E3%82%BF%E3%83%BC%E5%89%B5%E9%80%A0%E8%AB%96&display=&sort=

>>1529584 (OP)
https://z-library.sk - pirated books, probably
https://www.aozora.gr.jp - public domain books

https://z-library.sk/s/%E3%83%9E%E3%83%B3%E3%82%AC%E3%82%B9%E3%83%88%E3%83%BC%E3%83%AA%E3%83%BC?

>>1529618
I wasn't able to find any of the example books there, but thank you.

>>1529637
You are welcome. When pirating Japanese content, AFAIK, if English-language sources fail you, the only alternatives are Chinese ones. https://en.wikipedia.org/wiki/File_sharing_in_Japan
>Unlike most other countries, filesharing copyrighted content is not just a civil offense, but a criminal one, with penalties of up to ten years for uploading and penalties of up to two years for downloading