Short answer: you can't.
Long answer: Apple allows people to purchase/download Mac OS X in 1 of 2 ways:
-- buying a new Mac (desktop or laptop)
-- upgrading an existing Mac with a newer version of OS X than what it currently has.
They do *not* sell it or make it available for download for use on anything other than Apple-certified hardware, & those are only available from the Apple Store or from approved vendors.