Installer App Missing from App Store So I am installing a new 1tb hard drive in my late 08 uni. This is a fresh install of both the hd and OS - I'll port any files I need at a later date. I'm running El Capitan on my current hard drive.

I need to create a bootable installer to first load onto the new hd so I can then install the OS. 

I'm instructed to download the "macOS installer app" from the App Store, but this app cannot be found. Nothing comes up in this search. At all.

I'm at an impasse at this moment. Does anyone see a solution or know the problem?
"macOS installer app" is Sierra, all prior OSes were "OS X". 

A unibody can't run Sierra [macOS].  

You need El Capitan [OS X], which can be downloaded from the App Store [though it's difficult to actually search for], especially kept live by Apple because of the 'break' in OS support that happened at Sierra. 

See Apple KB: Upgrade to OS X El Capitan which gives links that will open the correct location in the App Store app.

...or try this direct link