Gakken is a Japanese educational company. One of their products is a magazine called "Otona no Kagaku" (Adult Science) which comes with a kit to build a toy version of a mechanical or electronic device. Because they're part of a magazine, the kits are only available for a limited time. Here's some examples of the other issues' kits [5]. Some of the more notable ones are a wax cylinder recorder [6] and a gramophone kit [7].
[1] https://www.cdjapan.co.jp/product/NEOBK-2453544 https://www.amazon.co.jp/exec/obidos/ASIN/4057507221/gkp_shu... https://hon.gakken.jp/book/1575072200
[2] https://www.youtube.com/watch?v=EB8qtW19nf4
[3] https://otonanokagaku.net/magazine/vol46/index.html
[4] https://www.turntablelab.com/products/gakken-easy-record-mak...
[5] https://otonanokagaku.net/ https://www.cdjapan.co.jp/series/2993 https://www.adafruit.com/category/269