There is a Dutch Web Site that references Bonsai History in Europe, and it makes a statement that the first bonsai association outside of Japan was in 1962. Read below. The site in Dutch, so I translated the page and pasted it here in case it gives you info you are looking for.
Bonsai geschiedenis in Europa | De Bonsaihut
Bonsai history in Europe
According to the earlier literature, there was only a few interest in bonsai in Europe in 1909. In that year, a Japanese businessman, a certain mr. Sato, a collection of trees to a London exhibition. Most of the trees sold there died because no one knew how to take care of them. It was not until 1950 that the first information on the cultivation and maintenance of bonsai was released. Not because the Japanese wanted to keep this a secret, but because all their writings were in Japanese and never been translated before.
In 1962, the first bonsai association outside Japan was founded in America. This example was later followed in many countries, resulting in growing interest. In 1972 a collection of bonsai was on display at the Floriade in the Netherlands. As a result, a number of enthusiasts gathered and the Dutch Bonsai Association was founded. Pioneers at the time were Han Donkel, Maud Wesselo, Gerrit Lodder, F. Braun, F. Verschuren, J. Maris. Daan Giphart was also there to my knowledge at the time. Other names that may sound familiar were Ad Pijnenborgh, Bert van Wageningen, Ed de Groot, Daan Goekoop and Lars Z. de Liefde.
The first larger bonsai exhibition in Belgium took place on 2, 3 and 4 April 1976 at the Novotel in Antwerp. In that year the Belgian bonsai association was also founded, and pioneer at that time was Danny Drowart. In that year there were about 300 members in the Netherlands, and just over 100 in Belgium.
In 1977 it was decided to set up a local department “Flanders”, and in 1978 the Flemish Bonsai Association was a fact. At the first meeting in Aalst on 24 September, 13 ‘bonsai pioneers’ were offered. The first theme at that meeting was the hoarding of plants in a bonsai bowl. At that time there were virtually no bonsaischals to be found in Belgium! More famous Belgian names who appeared on the scene were Agnes Muylaert-Luycx, Robert Windels and Marc de Beule.
The first bonsai nurseries such as Lodder Bonsai and EDO Plant also got off the ground. And in the early 1980s, the first books translated into Dutch appeared on stage, such as Joan Melville’s “Boom in pot,” “The Bonsai Book” by Koide - Kade and Takeyama and “The Practical Bonsai Book” by Han Donkel, which was a translation of The essentials of bonsai. Reference books from America, by John Naka and Will Valvanis, among others. Terms such as Saikei and penjing also appear on the scene, after the Ghent florals of 1980. In Eernegam, IMBO is creating a bonsai wholesale and retail import business. The right year is not known for sure.
Room or indoor bonsai make the hobby gain popularity. And imports from Japan are starting to become available easily. At the Floriade of 1982, Belgium and the Netherlands will exhibit 14 days of bonsai. They will receive about 50 square meters and an instructional videotape will be shown. Bonsai center Heidelberg is also becoming a household name in the bonsai world.
In 1982, 10 years after its founding, the NBV had about 500 members. Due to publications, exhibitions and the Floriade, the popularity of bonsai is steadily growing. There is a larger range of bonsai items on the market, which led to more sales, and then again more popularity. However, the first adverse effects also appear. Because of the greater awareness, people also realize that bonsai can be worth money and the first reports of theft are coming in at the associations. Books such as Bonsai Techniques 1 and 2 by Naka, and translated works from Japan, are now available in Belgium and the Netherlands.
Working groups and inspection systems are created. The first bonsai nursing calendars, tree species discussions, fertilization schedules, equine remedies against diseases, etc. are a fact. Bonsai is now also becoming more well known to the wider public. In 1985 the series “Boom in the Sun” was started, in which the specific characteristics of certain tree species were discussed.
FoBBS (Federation of British Bonsai Societies) was created in England in 1983 and a European bonsai association was first discussed. The following household names appear on stage: Peter Adams, Dan Barton, Craig Coussins, Harry Tomlinson, Peter Chan. At the invitation of Paul Lezniewicz, bonsai delegates from countries such as Germany, England, France, Luxembourg, Switzerland, Spain, Italy, the Netherlands and Belgium will meet at the first European bonsai Convention in Heidelberg, to discuss informally the origins of the European Bonsai Association.
Further contacts will take place at the first Bonsai Congress or Asociacion Espagnola Bonsai in Valencia. During the second British Bonsai Convention at Keele University, a general concept for the future association was conceived. One of the coordinators was Marc De Beule. The first annual meeting of the EBA was in Mannheim, and a committee was set up. Peter Brown as President, Marc De Beule as Secretary, Cees Doppenberg as Treasurer. With the aim of making everything formal, the EBA was founded on 24 September 1984.
In 1989, the first World Bonsai Convention was held in Omiya, Japan. The World Bonsai Friendship Federation is created. The first bonsai magazines appear. The first Dutch-language bonsai magazine was published in September 1994, under the name “Het Bonsai Blad”. Let this pass to Bonsai Europe and later in Bonsai Focus. In the late 1980s, early 1990s the following names appeared: Chye Hock Tan, William Vlaanderen, Marc Noelanders, Danny Use, Gijs Meboer, Farrand Bloch, Hotsumi Terakawa, Pius Notter, etc.
From now on you can take courses almost anywhere, and bonsai is now really accessible to everyone.