Sony typically updates the PlayStation Store on Tuesdays in North America and Wednesdays in Europe, which would place the release dates for the Grounded Bundle at May 6 in North America and May 7 in Europe.
The Grounded Bundle is the last piece of DLC for the Last of Us season pass, which costs $19.99. The package includes the new single-player difficulty level, Grounded Mode ($4.99 by itself); the Reclaimed Territories Map Pack ($9.99 by itself); the Survivalist Weapon Bundle ($5.99 by itself); and two Survival Skills bundles ($3.99 each by themselves). Sony will stop selling the season pass after the week of May 13.
For more on The Last of Us, check out our reviews of the original game and its single-player expansion, Left Behind. Naughty Dog is working on a "remastered" PlayStation 4 version of The Last of Us that is launching this summer.