I quit buying streamliners when they switched to plastic. All mine are Lionel aluminum cars. OK Engines still makes aluminum passenger car kits in O gauge. They'll make them any length and just about any window arrangement, smooth or fluted sides. Old Herkimer line.
Update - I acquired a beautiful 7 car set of the 18" K-Line cars from Doug here on the Forum. He had installed LED lighting, added more passengers, and a scale coupler at the rear. I'm really happy with these..