I'm a high school trombonist getting into composition. I've been writing stuff for a few years now, and I was posed a task by my band director to right a polka out of a piece I wrote this year. Problem is, I know next to nothing about polka other than duple meter. My first question is, what would the instrumentation look like for a small polka band?
I’ve played some Polkas duting military service. I played in a brass band. But the army also used to have harmony bands with wood wind instruments.
The most traditional instruments used to play music for this Bohemian dance include trumpets, tubas and clarinets, but contemporary bands also mix in guitars and percussion.
As you can see in this link one of the most important instruments is the accordeon:
Althoug the title of your question asks for the traditional instrumentation, I assume that's not what you want to know.
In case my assumption is wrong: The polka originates from Bohemia and is a vivid dance. So the original casting were small bands within families. This included instruments like violin, zither and bagpipes. But as said, I assume this is not the instrumentation you are looking for.
So let's switch to your question, where you mentioned "small polka bands". Here I assume you ask for a casting of wind orchestras (as a very small form of marching bands and so on) as this is the instrumentation which envolved in the following times. Here I found a source in German which explains the function of the various instruments: The melody is carried by the bugles to get a smooth sound. (Also trumpets do not harm.) Furthermore you have three clarinets as well as trombone and french horn. These instruments play the Nachschlag (after beat) which is responsible for the Gemuetlichkeit of a polka. Additional of course you need the typical bass with tuba