I would Assume the Stadium from number 1 is located somewhere in the Kanto region and the one from number 2 is Located in Johto, I am mainly going of the fact that Stadium 1 and 2 follow the Pokedex's of Gen 1 and 2.
As to where specifically in each region it's located I would have no idea, Maybe it's somewhere near the Pokemon League/Indigo Plateau. Just mainly because the games showcase gym leaders and E4 from each game I believe, Or it could be possible that the Professor for each region Oak and Elm have a seperate Town/Area in which they carry out there research, maybe this is why there are minigames? Maybe we're led to believe it's a fun minigame when infact we are helping the professors learn more about the pokemon from their regions.
Good topic and it's going to be nice seeing some peoples views on this, I find Stadium 1 and 2 to be the best pokemon games outside of the main series.