As bonsai grows internationally, this can be a very cramped way to look at who is a "master."
It is true that Japanese-trained instructors offer advanced skills that can be considered the "gold standard" for bonsai around the world .HOWEVER, that can be an extremely limiting view of bonsai in the larger global picture. The Japanese work with only a handful of the thousands of tree species used across the globe. What works for a Japanese maple, will kill an American oak or bald cypress.
In the last few decades, regional and national "styles" have emerged to a certain extent, based on more "western" tastes and more importantly, species. Do a search on Walter Pall, Vaughn Banting, Dan Robinson, Nick Lenz, Kathy Shaner, Mary Madison and Ryan Neil. All of those folks are considered "masters" by most western bonsai folks. Not really because they know Japanese techniques (some are considered masters because they IGNORE Japanese techniques and esthetics in favor of a more Western taste), but because they've learned how to use new species, adapt techniques to them and, not least, make extremely fine bonsai images.
There are noted traditionalists that DO have a direct link to Japanese masters, however.
Bill Valavanis was taught by legendary Japanese bonsai master Yuji Yoshimura back in the 1970s. Yoshimura was the co-founder of the Nippon Bonsai Society. Apparently his father had been a samurai in Japan and also a famous garden designer.
Bill's firm grasp of bonsai and Japanese techniques and esthetics has had a huge influence on U.S. bonsai and has a direct connection to Yoshimura.
Not long ago, we had John Naka on the west coast who was tireless in promoting bonsai around the world. Although he was Nisei (second generation American) of Japanese heritage and studied in Japan for a time, he was an irreverent "master" who just liked good bonsai. He was granted a National Endowment for the Arts fellowship in the U.S. in 1992 and Japanese Emperor Hirohito awarded him The Fifth Class of the Order of the Rising Sun in 1985 for his work with bonsai and spreading the word. His influence, like Yoshimura's, is long and very deep in the U.S.
Rockm, of that list, only Kathy Shaner is a "certified" bonsai master. She has her Certificate. Boon does, too. Ryan should, but Kimura didn't want to bother with the paperwork since Kimura knew Ryan would be doing his work in the US where it wasn't required.
I'm sure that Bjorn will get one if he hasn't already. Tyler Shorrad just received his after studying with Shinzo Suzuki. Danny Coffee is continuing his apprenticeship with Mr Tanaka. That's where Juan Andrade and Peter Tea studied. There are several others whose names don't come to mind right now... (it sux getting old!). Matt Ouwinga was an apprentice several years ago.
We are suddenly getting a wave of guys who have recently come back from Japan armed with advanced skills that we just didn't know about in the past.
Big time bonsai in Japan is largely a family cottage industry. Family owned. Past down from generation to generation. Usually what would happen is two masters who were friends would trade sons for a few years when they reached a certain age. They would go work at their father's friend's place a few years. Then return home. This tradition still continues. Shinzo Suzuki's son just completed his apprenticeship with Kimora. So, in this way, as masters traded sons around, the best techniques became spread around. Each family retained their specialties, of course.
But in the past 20 years or so, the sons haven't wanted to go into the bonsai business so much. Or the masters started having fewer children, I don't know. So, there's been a shortage of apprentices. It's hard work. Low, if any, pay. Little time off. Late nights. High pressure. New apprentices don't work on trees. Maybe they get to water them. They pull weeds, mix soil, sweep the grounds, lift heavy objects, clean dirty pots, spray poisonous chemicals...
So. There's a shortage of apprentices. The master needs grunts to do the dirty work. HIS son won't do it! So, they finally started to let foreigners become apprentices. (Holding their noses as they did it! Lol!!!). As a matter of fact, I've heard that Kimura is in need of apprentices. Poor Shinji's son is commuting back and forth from his Dad's place to Kimura's! Working two places!
Now, all that said, the Japanese are clever! They have realized that silly Americans will PAY to come over to Japan and help do some of this work! So some gardens are offering "tourist apprenticeships". They would be something like the Intensive classes I've had with Boon, just 24 hours/day, and for longer periods of time. Any where from a week to several months.
There, that's about all I know to tell you about apprenticeships in Japan.