Vitamin D and Fish oil are all your gonna need, and thats if your cant get enough sunlight, I believe its 15 minutes in the sun is all the vitamin D we need a day. And fish because of the omega 3 content, and the fact its got a good amount of DHA which is alot more accessible than flax.
Dont bother with calcium just eat plenty of small fish, leafy greens and you'll have plenty of it. I really cant see the need for vitamin C, averaging out vegtables contain just under 100mg of vitamin C per 100 calories so all you only need to eat 60 calories worth of veg to meet vitamin C criteria, obvioulsy each vegtable has its own value but i wouldnt worry.
Now magnesium is an interesting one, technically you will not need to supplement it if you have a diet rich in veg, seafood and nuts as they're all great sources of it. However magnesium is seriously underated in a SAD, and you can accomplish alot from taken the occasional supplement, partially becuase it forms the base of most metabolic processes.