Ok i just checked the .CAR and seems Cougar is not linked to any default cars.
I just added SIM_PANTERA to the Classes line:
classes="SIM_FULL, SIM_GTC, SIM_NOBRIT, SIM_DRIFT, SIM_PANTERA, SIM_NOKING, SIM_NOLONG, SIM_GTC76, SIM_TOURING"
And fired up the sim, just chose the Pantera and the Cougar comes up with it. I didn't do a server test but car should come up now when you select the Pantera.
You're going to have to edit all the Cougars if you want them all to show, i only did one.
If i recall correctly this is a Altbierbude car right? They have their cars on their site edited differently.