This Track Okayama Circuit(Formerly Aida Circuit) hosted F1 in 1994 & 1995 and SuperGT,WTCC and was built in 1990. It'll be perfect for GT6.
Amen,it's probably a Perfect Circuit for Track Days,Racing in all sorts of cars and a good challenge + it's where Senna raced in his last race in Asia before his death.
I'm surprised this isn't in the game really. It's Japanese, it's on the Super GT calendar and it has hosted other series.