Where are the MacOS startup boot icons located? Where is the exact location of certain icons like the internal storage drive icon you often see in the startup boot manager and other boot icons like it located on MacOS?

MacOS Catalina 10.15.2
The specified directories

/System/Library/Extensions/IOSCSIArchitectureModelFamily.kext/Contents/Resources/
 and 
/System/Library/Extensions/IOStorageFamily.kext/Contents/Resources/

do indeed contain the .icns files used by the startup boot manager or at least it contains replicas of the .icns used.