I downloaded V8 supercars from this web site and when i unziped it it has gp3 after it also i have Grandprix3 and grandprix 2000 season add on pack i have also installed the patch INST GPX3 211and gp3_2000_nocd
In this case you need "GP3 Edit". You'll find it in the download section here. Install it, configure it (tell it the path to your game's exe) Open the *.gp3 file and click on export. Et voilĂ ! One drawback: Gp3 Edit just works with GP3 (better use v.1.13 than the original v. 1.00) and not with the Addon