Q: Item temporarily unavailable

Restart your computer while holding Command-Option-R to access internet recovery. Use Disk Utility to erase the hard drive and then reinstall the original Mac OS X.

You need to get replacement OS X discs from AppleCare. Your 2011 is too old for Internet Recovery and if you are using Mavericks I'd recommend doing a complete wipe using the new discs you need and then installing Snow Leopard, then install the Mac OS X 10.6.8 Update Combo v1.1 and then update to El Capitan.

rkaufmann87 wrote:

 

You need to get replacement OS X discs from AppleCare. Your 2011 is too old for Internet Recovery and if you are using Mavericks I'd recommend doing a complete wipe using the new discs you need and then installing Snow Leopard, then install the Mac OS X 10.6.8 Update Combo v1.1 and then update to El Capitan.

I disagree. Computers that can be upgraded to use OS X Internet Recovery - Apple Support  The firmware update should have been applied as part of a system update at some time.

Well you are right, the article indicates a mid 2011 iMac should work. When I attempted it on my mid 2011 27" I got the same message as the OP, hence my reply.

Shouldn't that firmware update have been applied during a system update? I could be wrong, but it seems to me that it should have been. Maybe the OP will respond and let us know if it worked for him.

Did  you select  Macintosh HDas the destination to install to?