You can here: https://ipsw.me/ find the old restore images (the image will be downloaded from Apple's server), which you from iTunes can use for the restore.
To use the downloaded .ipsw file, you hold down the "Option" key, then click "Restore iPhone" in the Summary page in iTunes. Here, you'll see a file browser menu pop up. Locate your downloaded .ipsw ...
The issue seems to be that you first need an original app/file/folder with that icon in order to Get Info and copy the icon to the intended destination.
I would suggest using Automator to create your own dummy "Application", assigning the icon. Once you have that application, you can copy the file to your Volume.
Rename your icon to AutomatorApplet.icns, ...
I ended up opening doing this:
Open the icns file in GraphicConverter.
Select Edit → Select All (or press Command-A) to select the entire image.
Select Edit → Copy → Copy (or press Command-C) to copy the image.
In the Finder, select Go → Computer (or press Command-Shift-C) to navigate to Computer.
Click on the hard drive you want to copy the icon to.