I am a member of the following organizations. They all publish (hard copy) newsletters, and I list the associated websites:
The A. C. Gilbert Heritage Society is mainly concerned with Erector and other Gilbert products, but Gilbert did own Meccano in the United States from about 1929 (do you know the actual date? PLEASE let me know!) through the Second World War.
The Canadian Modeling Association for Meccano and Allied Systems (CMAMAS) is, as the name implies, mainly Canadian, but there are several of us in the US they have let in (smile). Meccano is MUCH more common there than in the US. This organization has more of an emphasis on model building than the US organizations.
The International Society of Meccanomen (and women!) is, as you might guess, an international group. Some of the very best Meccano modelers are members (that does NOT imply that I am a skilled model builder!), and the magazine has excellent articles on building and other topics of interest to Meccano (and allied systems) enthusiasts.