I know that they implemented them into the game. It's been 2 years since I've got the game, but I deleted it from my phone. Just wanted to know how to get the Alolan variants in GO (i.e. Alolan Raichu, Marowak, or Exeggutor).
Alolan Rattata and Alolan Raticate: Available in the wild as a common encounter, while Alolan Raticate is available by evolving.
Alolan Grimer, Alolan Meowth, Alolan Sandshrew, and Alolan Vulpix: Available in 7km Eggs as part of the Gifts feature.
Alolan Muk, Alolan Persian, Alolan Sandslash, Alolan Ninetails, Alolan Graveler, and Alolan Golem: Evolved after catching their prior evolution in 7km Eggs.
Alolan Diglett and Alolan Geodude: Available in 7km Eggs and the wild as uncommon encounters.
Alolan Exeggutor, Alolan Raichu, and Alolan Marowak: Tier 2, 3 and 4 Raid battles as of July 19, 2018.