Sorry , you have to buy it, unfortunately. You could possibly find it online but that may give you a virus and then you'll have to pay a lot to get that fixed. The easiest thing you can do is save up a few hundred dollars, then take it to a local Best Buy and to the Geek Squad. They will likely do this for little money- usually $200 which is not that bad actually.
I did not do this- for I took my mac book to the local apple store and wasted 400 bucks. I was Furious to know Best Buy has it for half of that!!!

Don't make my mistake.