procure services of experts and consultants or organizations thereof, including stenographic reporting services, as authorized by section
3109 of title
5 and to pay in connection therewith travel expenses of individuals, including transportation and per diem in lieu of subsistence while away from their homes or regular places of business, as authorized by section 5703 of such title: Provided, That no such individual shall be employed for more than 130 days in any fiscal year unless the President certifies that employment of such individual in excess of such number of days is necessary in the national interest: And provided further, That such contracts may be renewed annually;