The head of an executive department, independent agency or establishment of the Government, with the approval of the President, may use from the appropriations available for printing and binding such sums as are necessary for the printing of journals, magazines, periodicals, and similar publications he certifies in writing to be necessary in the transaction of the public business required by law of the department, office, or establishment. There may be printed, in addition to those necessary for the public business, not to exceed two thousand copies for free distribution by the issuing department, office, or establishment. The Director of the Government Publishing Office, subject to regulation by the Joint Committee on Printing, shall print additional copies required for sale to the public by the Superintendent of Documents; but the printing of these additional copies may not interfere with the prompt execution of printing for the Government.