Skins from The Alpha Collection are not obtainable through the weekly drop.
The Alpha Collection is a Valve-made collection of CS:GO skins introduced on 19 September 2013. The collection consists of 6 consumer skins, 5 industrial skins, 3 mil-spec skins, 2 restricted skins, 0 classified skins, and 0 covert skins.
Alpha collection skins were available as part of Operation Bravo which commenced on 19 September 2013 and concluded on 5 February 2014.