TubeNet

From the Willson website (http://www.swissprofi.ch/willson/news.html):

DEG Willson and Dr. Brian Bowman have commissioned John Stevens to compose a concerto for euphonium and orchestra. The work will be premiered September 27, 2005 at 7:30 pm at Mills Hall on the University of Wisconsin-Madison campus by Dr. Brian Bowman and the UW-Madison symphony orchestra. Tentative future performances are planned at UW-Eau Claire and the 2006 U.S. Army Band Tuba and Euphonium Conference.

David Spies
Racine Symphony Orchestra
Willson Tuba Quartet

To my knowledge it's his first one for Euphonium, and he's previously written a concerto for Contrabass tuba and Orchestra called Journey, premiered by Chicago Symphony Orchestra and Gene Pokorny. I'm not aware of other concerti that he's written.