I was able to purchase through the Amazon US store using my US credit card (no VPN needed). The product page is https://www.amazon.com/gp/product/B0CK19DWHP/ (changing .co.jp to .com). It will show up on Kindle like other ebooks.
The legendary public bath was actually mentioned before in the 2nd part of the collab with Tonikaku Cawaii:
https://mangadex.org/chapter/1055353/
(The 1st part is here: https://mangadex.org/chapter/1055356/ )