I don't think it's a doujinshi. I think those character designs are official since the concept art was shown in the second popularity poll. Here, the wikia link. The spread in that link you sent is the same one here.
https://bokunoheroacademia.fandom.com/wiki/Popularity_Polls
OH I reread what you said. GEEZ. No, I don't think I've seen any DJs of that AU. :( Sadly...
Try your luck over here though. They've got all kinds of djs.
https://myreadingmanga.info/boku-no-hero-academia-dj/
Mostly hardcore ones but it's better than nothing.
That's where I've read the doujin's... T^T I thought it was an actual story coz there were lots of it., (kinda like a re-imagined story or some such, and from that doujins came out)
It's always like, Deku, Todoroki, and Tenya are from a civilized part and are researchers and Bakugou and Kirishima are from the wild part... ... It was really interesting, and the doujins have that same setting so I thought there was an official story with that kind of setting
(I hope I made sense coz even I got confused on what I just said, even though I kinda understood what I just said... I'm not right in the head aren't I?)
http://www.mangago.me/read-manga/boku_no_hero_academia/bt/hs_chapter-214/pg-2/
I've seen a bit of doujins bout this where they're like. ..in a medieval setting??? I would really love to read or even see more so... anyone have a list or know where to find the stories?