Not critical, but its bugging me.
I only know of one way to the safari extension gallery, ie, from the 'Extensions' tab in Safari's settings, More Extensions... button.
Is there anyway to navigate there directly in the App Store app?
Oddly enough if you open the App store app on your Mac and then type "Safari Extensions" in the search field, you will find a listing of all of the Safari extensions available from Apple on their app store.
I have never seen a built-in category for just Safari Extensions but this seems to work.