I have always gone to a "booth" at the Rastro on Sundays. The family has been there for over 11 years (at least) and offer a large variety of designs on plates, vases, dishes, bowls, pitchers, you name it, they have it. Most of their ceramics are from Talavera. And if you buy a few things, they do bargain/negotiate!
If you walk straight up from the end of Calle de Ribera de Curtidores (the main street) the "booth" is on the left side.