If it were me, I would get the proper stud from HD. Yo can never be sure what grade of bolt or metal you're getting from a hardware store, regardless of what they say. Getting the old one out could be a problem if it broke off flush with the fork. If there is still some of the stud sticking out, I would try vice grips first. If not, you may have to remove the fork and get it to a machine shop.
How did you break it off?