A good overall article explaining why yoga is beneficial for MS
http://www.nationalmssociety.org/Living-Well-With-MS/Health-Wellness/Exercise/Yoga This gives a good overview of the styles and lots of quick resources.
I like this whole page. And then if you click on the top link, they have teachers trained in teaching students with MS.
This is from MS Active Source (it gives a breakdown of how yoga helps each symptom and a 3-level DVD set, online videos of poses too)
This is a great book…it is the one I used to start my yoga practice!
The author's website
A chair yoga website where you can locate teachers
Wonderful yoga teacher. My best recommendation for restorative yoga (also known as Yin yoga)
This is a good article about using a chair for yoga