Reddit r/manga sporadically posts these chaps days before mangadex.
Good luck finding anything on reddit though, only reason I even knew was that I randomly saw chap 3 of this while browsing r/manga.
The user who posts the chapters early on r/manga is
dogeroi, the scanlator, who also uploads it to MangaDex. You can follow their profile on Reddit (which I linked) to see if they post any chapters. Alternatively, search "Anan-san" on r/manga to find them in case you weren't on Reddit one day and missed a chapter's posting. None of the methods listed above are ideal, but it is what it is.
And of course, waiting for the chapter to be uploaded to MangaDex is the far easier option if you don't browse/use Reddit frequently. However, the chapters might take a bit to get uploaded to MD. For example,
Ch. 2 was posted on Reddit about 24 days before it was uploaded to MD.