It goes by several names (Flobakks, Papelmedia, etc) and I believe it was part of the Korg M1 package. Originally sf2, but I converted in Plogue, though Aria may read it straight in from sf2.
Here’s an sf2 (free, register to download)
https://www.polyphone-soundfonts.com/en/files/21-vocals/222-korg-choir-ahhs
Demo here
I also found some choir WAVs but I have not checked them out – but am about to!