Unable to reinstall Mac OS X after disk erase

Dear Apple Community,

I have recently erased the HD drive on my 2011 MacBook Pro (original OS X Lion, upgraded to El Capitan) - needed a fresh start, remove bugs etc.

However, when attempting to reinstall Mac OS X, El Capitan is no longer an option. When , instead, I try to reinstall Mac OS X Lion (Version 1.0.34) , I am instructed that 'this item is temporarily unavailable' (see attached pictures).

Any advice on how can I reinstall Mac OS X (be that Lion, El Capitan or other) gratefully received. I have tried the various start up key combinations (option,cmd+r etc), including internet recovery, however I face the same dilemma described above each time.

Many thanks

Alex