Amtgard is a major fantasy boffer larp in the United States. It uses the common American convention of “chapters”. Which are clubs all playing by Amtgard rules. Allowing Amtgard to federate itself over a large area. Which it has done as it covers the US but also has some chapters further afield; such as continental Europe.
The Amtgard Larp Rule Books
Amtgard is large, developed and offers support for members. No surprise then that has it’s own library of books.
The link here not only gives access to the main rule book, but also supporting monster rules. Additionally there is support for chapters as well.