Not sure about this but if you are talking about Simplex/Mavic retrofriction shifters, I had trouble getting cables to fit even in the 80's. However, I have found some decent cables that fit them well at a reasonable price. They are packaged/sold under the name brand "InLine". I believe they are distributed by Seattle Bike Supply (http://www.seattlebikesupply.com/SBS_home.html).
Bob said:
Have cable ends for derailleurs and brakes changed much since the 70's? I know there are some funky new systems out there... but will the ends of current typical road cables still fit Weinmann levers and Simplex DT shifters?