@SakuraJizz: It's the same for Surugaya, the doujin in your link is sold out as well. Mandarake links are fine, even when the product is sold out the page still provides listings that direct you to all the other shops where it might be currently in stock. Surugaya is no better about this at all, in some ways it's worse. Normally it's not recommended to link to second hand store listings anyway, you either link to a doujinshi.org entry or directly to the author's shop if they have one. The former has been defunct for a while though and it's likely never coming back, but in 2019 when this book was uploaded it was very much active.