You could use a more general term like:
* A group of barbers
* A team of barbers
* A staff of barbers
You could also get creative and use something like:
* A hive of barbers (evoking their busy nature)
* A crop of barbers (referring to their profession)
* A trim of barbers (a playful reference to their work)
Ultimately, the best option depends on the context and the desired tone.