Mercedes, Audi, BMW, Porsche and you name it can be found under other Automotive here Other Automakers. Create thread there with you questions in a main section. You will notice there are dedicated sub-sections for some brands there and these are there for limited traffic.
Due to limited traffic and limited number of cars and thread it's under Automotive. Once we have atleast extensive number of active threads about these cars , a sub-section will be created.
on the side note BMW, Mercedes sections were there for few weeks but you never noticed. Admins dissolved it and moved it under others automotive as there was literally no traffic in it. That's the reason the more famous and active cars have been given dedicated section or sub sections.
Thanks