First off, we know that the Pokemon company, Game Freak, is in Japan. Players in Japan get priority to mythical events since that's where Pokemon is based. (Referenced from here)
Here's what we know about Zarude:
Zarude cannot be found through normal gameplay and the movie will be released (as of March) in Japan later.
We don't have information on when Zarude will be released in other countries but we can assume Japan will get Zarude first, and then the other countries will receive Zarude possibly through Mystery Gift.