Why not use the Tohoku region, as far as I know it was never used in Pokemon. I even found a G/S/C version of the map:Sendai isn't a region is is a city that as of 1995 had 971,297 people. Tohoku is the region
Tohoak
The Tohoak region (Japanese: トーホク / Tōhoku-chihō) is a region in the Pokémon world where the events of Pokémon Vega take place. It is home to 386 different species of Pokémon (most of which came over from Hoenn, Unova and Signet). Professor Holly of Porcelia Town offers the starter Pokémon known...
pokemon-vega.fandom.com
Tohoak Map (GSC Demake) by NiallHoenn on DeviantArt
www.deviantart.com