The studs are considered part of the timing cover hence why they are not sold separately. I have never seen one snap like that. Some force must have been put on it during some kind of servicing as they will never snap just driving the car. Maybe someone hammered them on or had the cover off or the engine lifted for some odd reason and did something to snap them.
About your only choice is to see if you can find a local junkyard with a junk engine they will let you pull the studs out of. If you absolutely cannot find anything locally I could potentially look in my scrap pile as I am sure there is a couple of timing covers in there and pull a few studs out for you and ship them to you.