The flags used by any and all State institutions, as provided for in this Act, shall be paid for out of the funds appropriated for the running expenses of said institutions, the same as other necessary supplies are bought and paid for, and the flags for use over court houses and public school buildings are hereby declared to be necessary supplies, and may be paid for out of the public funds of the respective counties or school districts. No State institution or agency may purchase any American flags or Illinois State flags except those manufactured in the United States of America.