The Secretary of the Interior is authorized to purchase from appropriations made for the benefit of natives of Alaska, food, clothing, supplies, and materials for resale, under such rules and regulations as he may prescribe, to employees of the Department of the Interior stationed in Alaska and to natives of Alaska and native cooperative associations under his supervision. The proceeds from such sales shall be credited to the appropriation or appropriations current at the date of the deposit thereof into the Treasury and shall be available for the same purposes.