Macbook Late 2008 no startup disk, and cannot reinstall os x

Hi! I’ve had this problem for four months now. I haven’t used my macbook for a while because of this and it has been quite a hassle. Apparently, I factory reset my Macbook and when I try to reinstall OS X, it says “This item is temporarily unavailable” and when I go check the startup disk, there is no option. What do I do? I really need the laptop for school.