Here are just of a few of the many excellent Theater Organ forums and societies I frequent:
A few of my favorite technical forums
Rodgers Theater Organ Users Group (Yahoo Group)
While not very active, this forum is a treasure of knowledge and a must read for any Rodgers Theater Organ enthusiast.
Active forums on a variety of topics; helpful people and rich expertise.
Societies dedicated to preservation and enjoyment of Theater Organs
American Theater Organ Society
Los Angeles Theater Organ Society