I found them! https://www.amazon.com/gp/product/B018A4E058/

Celebrations V8224212 Twinkling Lights Bulbs,20-Feet, Multi-Colored

Random twinkling, Red, Green, Yellow-orange, Blue, and Magenta (the picture and description does not mention magenta, but I ordered 4 strings of these and to my pleasant surprise they had magenta, too). On the 100 bulb strand, 10 bulbs twinkle randomly. In short, these are exactly as I remember from the late 70's/early 80's.