If the band doesn't supply them, then the horn players make them up as they go along. Someone leads, someone follows. There is generally a 'call and answer' or 'fill the gaps' process. Horns are different. Horns play together .
Horns play in a unison pattern and harmonize with each other and the rest of the band.
What I plan to do is start a 'horn chart' depository with FREE charts for horn players. I am compiling a list of charts that I have and will post them. If you have any charts that you wish to submit, please contact me by email at the link below. My hope is that making these charts available to all bands will promote the use of horn players.