Where the Commonwealth has made an agreement with a foreign country to supply to that country products required for the defence of the country:
(a) the use of a product or process by the Commonwealth, or by a person authorised in writing by the Commonwealth, for the supply of that product is to be taken, for the purposes of this Chapter, to be use of the product or process by the Commonwealth for the services of the Commonwealth; and
(b) the Commonwealth or the authorised person may sell those products to the country under the agreement; and
(c) the Commonwealth or the authorised person may sell to any person any of the products that are not required for the purpose for which they were made.