You can go straight to the document source: HERE IS THE DOCUMENTBeautiful. Thanks!
Duh, they do give citations for the original documents right there in paragraph 2 of the NY Sun article itself:
The documents - one dubbed a "circular" and the other a "directive" - were captured in 1971 and are part of a trove of material from the war currently stored at the Vietnam Archive at Texas Tech University at Lubbock. Originally organized by Douglas Pike, a major scholar who is now deceased, the archive contains more than 20 million documents. Many are available online at the Virtual Vietnam Archive and, as the election has heated up, have been the focus of a scramble for insights into Mr. Kerry's anti-war activities. The Circular and the Directive are listed as items numbered 2150901039b and 2150901041 respectively. Their authenticity was confirmed by Stephen Maxner, archivist at the Vietnam Archive.