(a) The county purchasing official shall establish and maintain a list of eligible bidders covering all commodities and shall furnish copies of it to all purchasing officials of the county.
(b) Any firm which desires to bid and have its name on the list of prospective bidders shall notify the purchasing official in writing of this desire, setting forth the class and description of commodities on which it desires to bid and the firm's qualifications as a responsible bidder.
(c) Every effort shall be made by the purchasing official to notify all eligible bidders before purchases are made.