Need help with download of Quartus II 11.0 which is no longer available on Download Center

Try this Internet Archive search:

https://archive.org/search?query=subject%3A%22quartus+11%22

You so know that 13.0sp1 is still available as an official download:

https://www.intel.com/content/www/us/en/collections/products/fpga/software/downloads.html?f:guidetmD240C377263B4C70A4EA0E452D0182CA=%5BQuartus%C2%AE%20II%20Software%5D

Updating to that official version would be highly recommended.