Been enjoying the Adepta centric stories, but they don't bother to list any chronological order on Black Library, so what do you folks suggest ?
There isn't really one
Warhammer 40k is not a single series - instead, it contains lots of unrelated books written by different authors. There are of course some small series following one certain group of characters i.e. "Gaunt's Ghosts" which follows one Imperial Guard regiment or various "Omnibus" books (Ultramarines/Iron Warriors/Blood Angels/whatever) or books that focus on certain important events like the "Horus Heresy". But in general, the books are unrelated and often even contradictory - for example, the primarch Alpharius has been killed in at least three different books (yet he might still be alive) or the same Space Marine Chapter Master being at the same time killed by Eldars and alive fighting Tyranids.
Looking at the official Black Library page I've found about 50 (some of the titles repeat itself with different translations, some might be false-positive) books marked as "An Adepta Sororitas novel" and, from the look of them, only 3 are part of a series ("Broken Saints" trilogy"), the rest seems unrelated to each other. So just take your pick and keep reading in Emperor's name!