The best place to start would be FAR subpart 25.5, which discusses the evaluation and award of foreign offer supply contracts. You may want to also check your agencys guidance, or your service supplement, such as the AFARS, the Army Federal Acquisition Regulations Supplement.

Both the FAR and DFAR have extensive guidance on trade agreements (FAR subpart 25.4) that allow contracting officers to waive Buy American Act  requirements and purchase goods from foreign sources. See exceptions at FAR 25.401. The contractor must come from a country that the US has a trade agreement with (see FAR 25.402 for a list of trade agreements, associated countries, and dollar thresholds for supplies, services and construction).