They have links. They list therapists. They hold conferences for professionals (that I believe are open to multiples). They're famous for this stuff. They have professional publications. I have no personal experience with them whatsoever.
You can get one free sample issue of their newsletter. They take submissions for articles and artwork, they have links, a calendar, etc. and seem pretty friendly. The newsletter appears to be a laser print 8.5x11, 16pages, with 3-hole-punch for easy storage in a binder, and prints every other month. If you submit articles or artwork, you get the issue they print in for free.
A UK website offers an intense and excellent overview of the various dissociative disorders and a great bulleted list of self-suspecting symptoms. Available in non-printable booklet form by pdf, or one can order copies of the pamphlet from the site.