"Formerly prepared by the Interpretative Division, GCMs originally were the way the Office of Chief Counsel communicated legal advice in the context of private letter rulings and revenue rulings to the IRS assistant commissioner (technical), which eventually merged into the Office of Chief Counsel. After that, GCMs became the formal legal opinion of the chief counsel responding to inquiries from a National Office function outside of chief counsel or explaining the legal basis for the position taken in a TAM, letter ruling, or revenue ruling . . . GCMs are rarely written anymore except to repeal old GCMs" (IRS Guidance 1980-2003: An Ever-Changing Landscape, Tax Notes)
General Counsel Memorandum=Gen. Couns. Mem. or GCM
Below are links to select sources offering general counsel memoranda.
The following citation resources may be informative.