You can now download a pdf version of the entire vol.1 and 2 of the Progressive Method for French Horn on the "french horn method" page. This method also works well for trumpet beginners. There might be a few exercises going too low for trumpet but it mostly works. Of course, you can always buy the book itself on the "order books" page!
There be will pdf versions of vol. 1 for trombone, tuba and euphonium available soon.
Check it out!
I am associate principal horn of the Singapore Symphony Orchestra and the author of the progressive methods. I'm happy to share my experience as a horn player and teacher with you.