If you were not aware and you got the game there is a Rockruff internet mystery gift.
This provides the Rockruff needed to get the Dusk Lycanroc, though the thing is that it can be male or female.
I do not know if I can breed it to get a male with Own tempo, but I train and battle with male pokemon, so with this one being female, I won't keep it in my team.

Soooo I was wondering if there might be some friendly soul out there who is either seeking a female Rockruff and would swap, or perhaps doesn't care and will trade either way. I only ask because.. Yeah. I'm picky about my team. XD