There are authorized to be appropriated such sums, but not more than $200,000, as may be necessary for acquisition of the land described in section 407m-3 of this title: Provided, That the Secretary of the Interior shall not obligate or expend any moneys herein authorized to be appropriated for acquisition of the land unless and until commitments are obtained for donations in an amount which in the judgment of the Secretary is sufficient to provide a replica of the Graff House in accordance with section 407m-4 of this title.