The SpA training spot is actually on the top floor of that building, where you fought the Ditto-Arceus; not the grass at the bottom. You also want a bunch of -Att berries so you can kill the unowns and make SpA ev grinidng a lot faster.
I just spent an hour headbutting trees hundreds of times in crysolia forest, and not a single pokemon showed up. Is there a specific weather required or something to catch a chatot?