To help you a bit I have gone through a Formula 1 almanac and made a list of all drivers who appeared in Formula 1 races until ca 1999, and which I can not remember seeing in the game.

From the point winners 1991-1999:

Jarno Trulli
Marc Gené
Esteban Tuero
Tarso Marques
Juan Pablo Montoya

Other:

Toshio Suzuki
Marco Apicella
Domenico Schiattarella
Esteban Tuero
Stephane Sarrazin
Alex Yoong https://en.wikipedia.org/wiki/Alex_Yoong
Gastón Mazzacane https://en.wikipedia.org/wiki/Gast%C3%B3n_Mazzacane

I hope this helps add a few lesser known drivers.

I also went through a list of CART and Indycar Champions (born between ca 1960 and 1980)

Bobby Rahal https://en.wikipedia.org/wiki/Bobby_Rahal
Jimmy Vasser https://en.wikipedia.org/wiki/Jimmy_Vasser
Gil de Ferran https://en.wikipedia.org/wiki/Gil_de_Ferran
Cristiano da Matta https://en.wikipedia.org/wiki/Cristiano_da_Matta
Sébastien Bourdais https://en.wikipedia.org/wiki/S%C3%A9bastien_Bourdais

Buzz Calkins https://en.wikipedia.org/wiki/Buzz_Calkins
Scott Sharp https://en.wikipedia.org/wiki/Scott_Sharp
Tony Stewart https://en.wikipedia.org/wiki/Tony_Stewart
Kenny Bräck https://en.wikipedia.org/wiki/Kenny_Br%C3%A4ck
Buddy Lazier https://en.wikipedia.org/wiki/Buddy_Lazier

And a list of active drivers in 1990, who may as well be of interest as a starting point

https://en.wikipedia.org/wiki/1990_CART_PPG_Indy_Car_World_Series