Finding a high quality mixte can be a real challenge. Most made between the war and the mid seventies were entry level stuff and ride alright but were not the high end tubing of the time; Reynolds 531 or Columbus. Motobecane Grand Jubilee and Raleigh Super Course Mixte's were both made from 531 tubing, but are really hard to find. Most of the mixte frames out there are really good, are built around touring geometry and ride really well. My son has a Raleigh Gran Prix that he likes. You just have to search. These days, Soma produces the Buena Vista frame and Rivendell produces the Betty Foy, other than those, I don't know.

Marc