For the non-DIY tire types, Peter White in New Hampshire has all the studded tires (and lots more goodies, including excellent lights) his sometimes amazingly thorough, sometimes opinionated, sometimes annoying, sometimes wonderfully humorous, sometimes a wee bit out of date website: http://www.peterwhitecycles.com/
They will want the erto number off the side of your current tires when you place an order just to make sure they send the right diameter tire.

Order tires well before the snow flies to help make sure your order doesn't end up back-ordered. For lights, it's probably already too late to avoid the fall standard time rush for upgraded lights.

+10 for the winter cycling forum and SixteyFivers links.