The Windmill Study Unit is a part of the American Topical Association and publishes a regular bulletin called Windmill Whispers.
It's a international group, which although primarily philatelic, also attracts members who belong for the interesting molinological
items that are carried in the bulletin.
The unit has a
new website, which includes back issues of Windmill Whispers to give you a taste of
what they cover (which includes as well as stamps, items such as matchboxes, phone cards, coins and banknotes, sugar bags), and also
has
full contact details of the representatives in various countries.