How to buy OS X Yosemite on unsupported Mac

Hi!

A family friend recently gave me their 2009 MacBook A1181- with no hard drive. They had bought it on eBay with no HDD and gave it to me with a $100 to get a hard drive. I bought a SSHD an installed it. It worked perfectly. I want to install OS X Yosemite on it- as far as I am aware it is compatible- but I found I could only obtain it from the App Store. I own a 2006 iMac running Lion and could not complete my purchase because my Mac is unsupported.

So how can I obtain Yosemite legally not through the App Store? Should I call Apple? Should I go to an Apple Store? What should I do?

Thanks,

rmich1731