take a hammer, whack out the old stud.... ,
insert new stud from back of the hub... find some huge washers and put new lug nut onto partially inserted stud, tighten down lugnut as much as possible.. it really helps if you have a friend here because that new stud is going to have to be forced into the hub, just start cranking down on the lug nut to pull the stud into the hub..
keep going untill back of stud is bottomed out
thats my best directions i can give you
as far as where to get a stud, go to the auto parts store, just tell them your car and say hey, i need a new stud and lug nut, probably 3-5 bucks for both.