Well, this is unofficial data, but I was bored so I did an experiment.
I bred a legit Own Tempo Rockruff with Jolly nature (I know it is legit because it was traded to me by a friend) with a Sassy Ditto holding an everstone. I mean, I could’ve found this on the web.... but I was really bored :P.
So what happened was I got 3 female Own Tempo Rockruffs with Sassy as their nature. I did the experiment because I wasn’t sure if Ditto could pass down their nature via an everstone, but it worked.
So I would say take the Adamant Ditto and give it an Everstone. Breed it with the Moxie Salamence and you’ll eventually get an Adamant Sheer Force Bagon.
Note that this is in Ultra Sun. Hopefully the breeding mechanics are the same :P
Of course, there are other ways to do this, but I’ve found that this is very efficient.
Hope this helps! :)