When changing the icon of the Hard Drive in MacOS - where are the icns-file actually stored?

Long story short - I bought a new computer and decided not to do a migration from my old Mac to the new one. Still - there are some things I would like to keep and the icon I found years ago to replace the "Macintosh HD" icon is something I very much would like to find.

So my question is - where are these icons actually stored? I've searched "everywhere". It's not in /System/Library/CoreServices/C­oreTypes.bundle/Contents/Resou­rces where the system icons is stored.

Anyone out there with the same level of OCD as me who can help me out?

I'm running Catalina 10.15.1 if relevant.

First of all: Custom icons that you use to override System default ones will never be stored inside /System/Library/.. as this is a System reserved folder.

On macOS when you paste a custom icon to a folder or file using the Finder Info panel these are stored in the resource fork of the extended attributes of a file/folder.

Now regarding your use case: In order to see these you need to show the hidden files and you will see .VolumeIcon.icns on your / local drive (Macintosh HD): As this is a write protected path (SIP) you cannot store custom data there and instead this .VolumeIcon.icns alias is there and will point to the actual icon file.

If you are still not able to locate the icon file you can always use this next trick. Open the Finder "Info Panel" for your MacintoshHD that has the custom icon and click on the icon representation and copy it to the clipboard (cmd + C) and then open Preview and select "File > New from Clipboard" and then save the icon as icns. Done!