Can't download ESXi 5.5 ISO - needed due to an old server

Hi,

As the title states I am unable to download the older version (5.5) of ESXi. I need it due to compatibility issues with the server I want to use as a test machine.

A new server is not an option, due to personal constraints.

Config:

HP ProLiant DL380G6 with an Intel Xeon 55xx Series CPU.

Any help is much appreciated!