Mo. Rev. Stat. § 8.280
Every commission, board, committee, officer or other governing body of the state, charged with the construction or repair of public buildings, and every person acting as contracting or purchasing agent for any commission, board, committee, officer or other governing body of the state, shall purchase and use only the products of the mines, forests, and quarries of the state of Missouri, when they are found in marketable quantities in the state, and all materials contracted for shall be of the best quality, and preference shall be given to Missouri materials and labor where same are of a suitable character and can be obtained at reasonable market prices. Any contract for materials made in violation of this section is void and in the event of the construction or repair of public buildings where products of mines, forests and quarries other than as enumerated above are used, the commissioner of administration shall not approve, the state auditor shall not audit nor the state treasurer pay any warrants issued in payment of the construction.
§ 8.280, RSMo