Greg Calvert's two books on the New Left are:
A Disrupted History: The New Left and the New Capitalism, by Greg Calvert and Carol Neiman (also a former Rag staffer), published in 1971 by Random House and now out of print.
Democracy from the Heart: Spiritual Values, Decentralism, and Democratic Idealism in the Movement of the 1960s, published in 1991 by Communitas Press. Available from Communitas Foundation, P.O. Box 4542, Albuquerque, NM 87196.
Greg published numerous articles, many of them in "New Left Notes" and "Liberation."
Probably Greg's most important and widely-quoted speech was given at Princeton University, in February 1967. It has been reprinted in a lot of different places, including Massimo Teodori's book, The New Left: A Documentary History, published by Bobbs Merrill 1969.
There is also a series of interviews with Greg in the archives of the Columbia University Oral History Project.