Ryan Neil (Bonsai Mirai), Peter Warren (Saruyama), and Bjorn (Eisei-en) all have excellent material that is available for free on youtube, although I would recommend donating what you can to support their excellent projects and production costs.
I know that this video in particular has been helpful to a lot of people:
The official channel of bonsai professional Bjorn L Bjorholm! Watch bonsai vlogs, demos, and instructional tutorials all about bonsai art. Our Bonsai-U free ...
www.youtube.com
He also offers an online course through Bonsai Empire that do have a fee but they are pretty reasonable IMO
Its probably not a live course, but some videos you watch
Course introduction Bonsai is an art-form that has been around for thousands of years. Although it's a highly rewarding hobby, too often it is seen as difficult...
Course introduction Introducing the Bonsai Intermediate Course, an online tutorial featuring the best of contemporary Bonsai design and the techniques needed to...
The Advanced Bonsai Courses from Bjorn Bjorholm and Bonsai Empire break down advanced concepts into bite-sized techniques you can use on your own trees.