The Secretary of Health and Human Services, in connection with existing authority (except section 254b ¹ of this title) for the provisions of health services to domestic agricultural migratory workers, to persons who perform seasonal agricultural services similar to the services performed by such workers, and to the families of such workers and persons, is authorized to arrange for the provision of health services to such workers and persons and their families through health maintenance organizations. In carrying out this section the Secretary may only use sums appropriated after December 29, 1973.