A 10k stone box is an item in Evony TKR (The King's Return). It can be found after killing certain monsters or bosses, with some of them listed below.
The description of 10K Stone Box in Evony TKR says:
Use it to gain 10,000 Stone.
10K Stone Box is known to drop from a number of bosses or monsters upon killing, including Zombie, Redcap, Centaur, Skeleton Dragon, Werewolf, Manticore, Yasha, Peryton, Minotaur, Griffin and Pumpkin Monster.
Note: This list may be incomplete.
10K Stone Box is known to potentially be obtainable from opening Medium Alliance Boss Package. The links for each item are below:
Note: This list may be incomplete.