Mac OS X Lion

I am cleaning my Mac for the first time in about 7 years. I have erased the hard drive and trying to download Mac OS X Lion.

Though when I "Sign in to download from App Store" a new box appears and says "this item is temporary unavailable". Therefore I can't take this any further.

I'm sure I have the disc somewhere, but I'd rather just try and crack on without.

Any help please?