Are there any directories of the official icons used in macOS? Things like the share sheet, the forwards and backwards glyphs, the magnifying glass, etc. are standard across macOS.

Is there any official repository of these glyphs? It would seem to be extremely useful.
Most of the icons are in the System folder. Just enter the System Folder, hit Cmd+F, click +, select Kind in the first dropdown box and Image in the second. This should get most of the icons.

Others are in the Apple Symbols font, as Tom pointed out.

A few more can be found here: /System/Library/CoreServices/CoreTypes.bundle/Contents/Resources.