Prelude and Allegro for Two Euphoniums and Piano

You can get the music on this page of the IMSLP.

If you want to play this with a computer-generated piano part, you can do it through these links:

Here's a link to the piano part for the Prelude
And here's a link to the piano part for the Allegro

You can also listen to the full Prelude here, and the full Allegro here.