Try the Company of Military Historians (http://www.military-historians.org/). They have a forum which addresses a number of subjects and a lot of true experts who can guide you through US-military research. The Company is 50+ years old and boasts 1600 members. It's quarterly Journal is possibly the best magazine going if your interest is US uniforms and insignia. I am a Governor of the CMH and write the occasional article on Canadian topics in order to educate the membership.