Here are a few options that are often used, depending on the context:
* A board: This is a formal term used for a group of leaders, particularly in business or organizations.
* A caucus: This term is often used for a group of leaders within a political party.
* A committee: This is a general term for a group of people assembled for a specific purpose, which can include leaders.
* A council: This term can refer to a group of leaders or advisors, often in a political or religious context.
* A group: This is a very general term that can be used for any collection of leaders.
* A hierarchy: This refers to a structured system of leadership, with different levels of authority.
Ultimately, the best collective noun to use depends on the specific situation and the type of leaders you're referring to.