British Trombone Society
Well, if you haven't already guessed by now, the British Trombone Society,
formed in 1985, is a properly constituted association for trombonists,
organised by a central committee with representation in all regions
of the UK.
Trombone Page of the World
A large portal to all things trombone.
International Trombone Association
The general purposes of the International Trombone Association shall be: to promote communications among trombonists around the world to improve the artistic level of performance, teaching, and literature associated with the trombone family to function as a clearing house for trombone-related ideas and information.
Trombone History
All about the history of the trombone.