How can I get a Zeraora in Pokemon Ultra Moon?
Solution 1:
As of when I'm writing (2018-04-25) it has only just been officially revealed (though it's existence was discovered by data miners) and is unobtainable using legitimate methods.
It will probably be distributed through an official event or in the next games.
As a side note, you do not require Zeraora for your regional Pokédex to be considered complete so there isn't much point in getting it early.