Knives,
Mechanical (car, airplane, race car, diesel, tractors...)
Outdoors ( hiking, backpacking, camping, Jeep)
Machinists ( tool and die, engineers, CAD/CAM)
Horses
Farm/Ranch
Old Radio/ tube electronics
Political ( certain ones)
Women's forums ( some )
Religious ( Zion's camp, Mormons, and teachings of self reliance, good info there)
These will surprise you:
Recovery programs, for instance 12 step based ones for alcohol and substance abuse, with forums , discuss firearms. Be it self reliance, getting into hunting , shooting sports and the like. Men and women getting past a bad deal, learning to live life and participating with each other in these firearm activities.
I know, quite a few folks, men and ladies I have invited out, and assisted with.
Medical forums.
Yes there are forums for Medical folks that have been in trouble with alcohol and substance abuse too. While they do attend 12 step programs, they also have special programs for Doctors, and Nurses. Some additional ones are for Rad Techs and other jobs like Bio Med.
Associations. By this I mean for instance Nurses, do not agree with Nurses Assoc and views on firearms, or other policies. They do their job, still they get together to keep current on new regs, regulations and medical stuff, like Continuing Credits.
Men and Women, and they also share other matters like activities...many are shooters, they invite others, and discuss various aspects of firearms, from different sports ( trap, skeet, IDPA...etc) to RKBA.