Not sure if you're asking for info on what music is played in this cartoon or if it's been made available.
The piece that Mickey and his Orchestra try to play is called "Light Cavalry Overture".
Sadly Disney has not released the scores to any of it's short cartoons. The most we've ever gotten is the music from Mickey's Toontown and Toontown Fair at WDW, which are re recorded versions of the scores to several Disney shorts. This particular piece is not used though. Hope that helps.
Incidentally my favorite part of that cartoon is when (I think it's) Donald is desperately trying to play the accordian, and it just keeps going all over the plays and only makes a "Hee-Haw" sound, albeit, in time with the music. Classic.
Actually, that piece of music was released on an old LP set called "The Magical Music of Walt Disney". It was released in 1978 as part of Mickey's 50th celebration. It was a wonderful 4 LP set that covered everything from the early Mickey shorts all the way to the theme parks.
The "Symphony Hour" portion is on the first LP as the last part of the Mickey shorts section, right before it moves on to the silly symphonies. This LP set was also the only US release to include part of the "Mickey Mouse Revue". Until Randy came along and gave us the 75 Years of Music & Memories set, this was the most comprehensive set availible.