Reinstalling OS X Yosemite

I purchased a computer from a friend. MacBook Pro (Early 2011) it had 10.10.4 OS X Yosemite on it.... when i tried to do the reinstall on it after the step of signing in to app store for verification it tells me " This item is temporarily Unavailable." I now know that Yosemite is not avalible at the app store... ok fine.... what do i do to get this Mac Book Up and running.

(Yes I am new to Apple Software...... love the products but finially playing with the software please be kind ill catch on fast)