It's very simple to access those models through making a custom TXT file with the following content:
"ReplaceableTextures\CommandButtons\BTNOrcCar.blp
ReplaceableTextures\CommandButtons\BTNDwarfCar.blp
ReplaceableTextures\CommandButtons\BTNDiabloCar.blp
ReplaceableTextures\CommandButtons\BTNUndeadCar.blp
Units\Other\OrcCar\OrcCar.mdx
Units\Other\DwarfCar\DwarfCar.mdx
Units\Other\DiabloCar\DiabloCar.mdx
Units\Other\UndeadCar\UndeadCar.mdx"
Then opening Warcraft III Viewer, opening War3x.mpq, then opening the "File" tab, choosing "External listfile" from there and choosing the .TXT file. Then you have full access to all car models.