To find Wendice the player must have spoken to the "Huntmaster" in Phon Coast and defeated Thalassinon, which will trigger the start of the Rare Game quest. The player then has to kill three or more Wendigos before the Wendice will spawn.
After killing the required number of Wendigos, it will spawn in the center of Destiny's March. The easiest way to do this is to run around the diamond shape of Destiny's March killing all the Wendigos around, and soon a red dot shows up in the center. It seems that the player has a certain amount of time to kill the Wendigos, so it is best not to waste time running around.