Here are the remaining two Shards, Grixis (black) and Jund (red) that Wizards previewed last week. The other Shards that were previewed were Naya(green), Bant(white) and Esper(blue). Check out the wallpapers below.
Grixis (previewed August 14)
Jund (previewed August 15)
Download these wallpapers through Magic Arcana archive. Click here.