In that case, you probably have to pick it up from rumbling. I
don't think it comes in egg form since Pokemon can be in either egg
form or already hatched when they are found during rumbling. If you
don't have the Alola rumble area, check in on the daycare owner
until he gives you a quest and see the quest through. He'll give
you the area. (It's not a map like some of the other special
areas.) I don't know what trainer level you have to be before he
will give you the quest.
(The quote was from Bulbapedia, but some things work differently on
here.)