What is a wish stone in Pokemon Mystery Dungeon explorers of time?

Unfortunately, you cannot obtain the Wish Stone again after you have lost it. The item is obtained as a reward for a special mission, and once you have lost it, you may not get it back, as the special mission has been completed.

This supports the theory that there is only one Wish Stone available per Rescue Team game.

all hope is not lost i heard that you can find another at wish cave floor 50