There are only four cars I know in Gran Turismo 4 that have more than six gears: The GT-R Concept (and then the race car - I think), the Nissan Skyline 350GT-8, which has... 8 gears. And obviously the Formula GT.
Are there any more?
The Nike One has eight gears, as well. But given the monster torque it generates even at 2000 RPM, there might as well be only one gear; keeping it in eighth is the fastest way to drive it. Beyond that car and the ones you mentioned, though, I don't recall any others with seven or eight gears.
Are you sure about that? CVT means Constantly Variable Transmission, meaning it accelerates by constantly widening the gear ratio, meaning there is only one gear. That's why it basically gets to a certain number of revs and from there it revs up very slowly.