In the description for purchasing the Potato Sack pack of games, it was stated (bold mine):
Plus, if you buy this pack (or have all 13 of these games in your account) you get a potato hat in Team Fortress 2! (Potato hat available after April 5th) and a special skin in Portal 2 co-op.
I purchased the pack, but when I go to the Robot Enrichment screen, there aren't any new skins for Atlas or P-Body. I also searched the ingame store to no avail.
Where, when or how can I get my special skin from preordering?