S1- Manpower (organizations)
(Note I have no affiliation with any of these groups, and list theme here because they may be of interest to like minded people for networking.

A Well Regulated Militia

My Militia.com

S2- Intelligence:

Forward Observer

Public Intelligence

S6- Signals

Brush Beater

AMRRON (American Redoubt Radio Operators Network)

Advanced Electronic Warfare and SIGINT: Association of Old Crows
(not for the technical novice)

S7- Training

Max Velocity

Mountain Guerrilla (John Mosby)

Mason Dixon Tactical (J.C. Dodge)

SHTF School