Put a different colored dot on each desk in a group. When you need to have one student from each table do something, you can just simply say "Green dots, come get the papers for your table." or "Orange dots, take your table's trash to the trashcan."
What are your expectations for students when working in pairs or groups? good management needs to be in place FIRST -You can make up your own -- teach this before working in groups! Post in the room and refer to it often!