The county superintendent of schools, or, when so directed by him or her, the county purchasing agent, shall, whenever a school supply revolving fund is established, purchase school supplies and equipment for the school districts of the county which are required or authorized to purchase supplies or equipment through him or her, and upon requisition therefor by the proper authorities of the district shall deliver or cause the supplies to be delivered to the district together with a memorandum of the amount of the cost of the supplies delivered.