The term is most commonly associated with Suzuki Roshi, who founded the San Francisco Zen Center. He has a book, "Zen Mind, Beginner's Mind." You can learn more about him here: https://en.wikipedia.org/wiki/Shunry%C5%AB_Suzuki
Finally, I have had the most special "beginner's mind" experiences while attending multi-day, silent meditation retreats. I live in the Bay Area, so I've attended Spirit Rock up in Marin. However, retreat centers exist all across the world. I recommend "insight" retreats, which are sometimes referred to as "mindfulness" or "Vipassana" retreats.