You will find most car manufacturers represented here (only one i couldnt find was Seat).

The second hand car market isnt vibrant in the newspaper classifieds. For used cars you have a few options.
1. Look at advertisements placed on boards in large supermarkets (eg Family Food Centre)
2. Cruise around the used car dealers along Salwa Road. (there are lots of them of varying standards)
3. if you are confident in assessing a used car, try the auctions in the industrial area on friday (risky but bargains can be found)

hope that helps