There are many in game trades that can help you get the original/different form.
In the sword and shield:
In Turffield stadium,Mattia wild trade you a meowth named cash for a Galarian meowth
Inside Ballonlea Stadium:Eve will trade you a Yamask named Masky for a galarian
Yamask
In Spikemuth,A Team Yell grunt called Edmund trades you a kantonian mr.mime called mymo for a obstagoon
In The Isle Of Armor:
Regina is a trainer that can spawn in literally everywhere she trades:
Kantonian Meowth
Kantonian Ponyta (Shield Only)
Kantonian Farfetche’d (Sword Only)
Alolian Exeggutor
Alolian Marowak
Kantonian Weezing
Kantonian Mr.Mime
Johtonian Corsola (Shield Only)
Hoenn Zizagoon
Unovian Darumaka (Sword Only)
Unovian Stunfisk
All for their galarian/normal counterparts
The diglett guy can also give you different Alolian forms