I don't usually seek it out, it just ends up finding me instead while I look for other things. The only ones I can think of at the moment are Fuka to Issho by Miharu, an Attack on Titan yuri doujin made by Amaro Tamaro, a Prison School doujin made by Fei, the most recent FFVII Yuffie doujin made by SGK, and some of the art that Rokuku has made.
Alot of them have other things about them though so you'd be disappointed if you were looking for just the showers. I think only the Miharu one and the Titan one have a good amount of panels dedicated to it, so that's what I mean when its stuff that kinda gets clumped in with other kinks because they don't want to leave anybody out.
Maybe I should just finish up Prison School instead, or catch up to the manga.