"Gray Market" Items

Is there anything in law or regulation that prevents vendors from selling, or the Federal Government from purchasing, gray market items?

For the uninitiated, gray market items themselves are perfectly legal (i.e., non-counterfeit) goods. The problem with them is that they are sold through channels not authorized by the manufacturer. Specifically, either the vendor is not an authorized reseller, or the manufacturer intended to sell the goods in specific foreign markets only, or both.