>>30548222If you don't have one of those 6V Dittos that have been floating around, here's what you do.
First, acquire two items: a Destiny Knot, which can be purchased at the Battle Tree for 48 BP, or alternately, acquired by a Pokemon with Pickup (probably the easier option). If held by a parent, this will pass 5 IVs between both parents to the offspring, whereas the usual amount is 3, I believe. You'll also want an Everstone (just use Thief on Roggenrola, they have a 50% chance of carrying) on the parent with the offspring's desired nature.
To get good IVs on a parent, simply SOS chain it. After long enough (I think about 40 steps), the Pokemon that get summoned are guaranteed 4 random perfect IVs. If possible, get a male and female in this manner, and make sure you check their IVs with the in-game judge (gotten from the Ace Trainer at the Battle Tree, accessed through PC) or with Serebii's calc (make sure you calculate everything as soon as you catch a Pokemon; you don't want unknown EVs messing with your data)
http://www.serebii.net/games/iv-calcsm.shtml (That calc won't be any good for newborn Pokemon since their stats are still too low to determine anything from)
Once you have two good parents, make them hold the aforementioned items and start hatching eggs (get a Flame Body Pokemon like Fletchinder to speed this up), keep checking the offspring's IVs until you get good ones, swap parents out with the offspring, rinse and repeat until perfect.
I made a visual.
