I see the CMP as being like the Post Office... started out as run by the government (DOD) and then privatized by Congress.
The law that Congress passed also authorized the CMP to sell surplus .22 and .30 military rifles ammunition and parts.
I don't know if the POTUS can unilaterally issue an executive order stopping them since I assume this was a bill back in 1996 that was passed by Congress and signed into law by the then POTUS (Clinton).
36 USC Chapter 407, Subchapter II - CIVILIAN MARKSMANSHIP PROGRAM
36 USC § 40728A - Recovery of excess firearms, ammunition, and parts granted to foreign countries and transfer to corporation
(a) Authority to Recover.— The Secretary of the Army may recover from any country to which rifles, ammunition, repair parts, or other supplies described in section 40731 (a) of this title are furnished on a grant basis under the conditions imposed by section 505 of the Foreign Assistance Act of 1961 (22 U.S.C. 2314) any such rifles, ammunition, repair parts, or supplies that become excess to the needs of such country.
(b) Cost of Recovery.—
(1) Except as provided in paragraph (2), the cost of recovery of any rifles, ammunition, repair parts, or supplies under subsection (a) shall be treated as incremental direct costs incurred in providing logistical support to the corporation for which reimbursement shall be required as provided in section 40727 (a) of this title.
(2) The Secretary may require the corporation to pay costs of recovery described in paragraph (1) in advance of incurring such costs. Amounts so paid shall not be subject to the provisions of section 3302 of title 31, but shall be administered in accordance with the last sentence of section 40727 (a) of this title.
(c) Availability for Transfer to Corporation.— Any rifles, ammunition, repair parts, or supplies recovered under subsection (a) shall be available for transfer to the corporation in accordance with section 40728 of this title under such additional terms and conditions as the Secretary shall prescribe for purposes of this section.