Apparently the Steam version blocks Ferrari and Porsche vehicles from showing up - even the ones that come with the game. I'm not sure why they did that but I found the fix:
1. Run the v1.1 patch (doesn't matter which region). When asked which directory your GTR2 is installed in change the folder to another location (a temp folder on your desktop for example) - the installer defaults to C:\GTR2.
2. When the v1.1 patch is installed copy net.dll and net_dedicated.dll from the folder you just installed it to, to your steam\steamapps\common\GTR 2 - FIA GT Racing Game folder (make backups of the two original files before copying the new ones if you want).
3. Copy no-cd .exe to your steam\steamapps\common\GTR 2 - FIA GT Racing Game folder (again make a backup of the original .exe in that folder if you want).
4. Run Steam. Enjoy Porsche and Ferrari cars.
This fix is courtesy of a user named Raven over at Gamer's Crib:
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