Is there an official Google Apps package?
Official GApps package is never available publicly. Google only provides it to authenticated OEMs like Samsung and HTC. It'll be installed only on Google Play Verified devices, in their stock ROMs.

That's why individuals can only download and flash unofficial GApps packages.

You can, of course, extract Google Apps from an authenticated phone and install it elsewhere, but you'll surely do extra job in comparison to flashing well-prepared packages.