Here's the locations for the chests scattered around The Sanctuary containing the chance for the top and bottom pieces of the bunny suit! Keep in mind that the chests are randomized upon opening, so you could get duplicates of either the top or bottom. You may also obtain tomes to gain experience, gems to change the stat-scaling for weapons, or nothing at all. However, the chests do respawn after a certain amount of time (usually every in-game night and morning) so pick any of the three you like and try your luck! (Sorry for the gifs being small...x_x)

• Here's chest one, top of the Sanctuary tower:
  You'll turn left at the end of this gif. There will be a platform you jump to where a hole to the outside will be. climb the spiral and there will be two mice with the chest in between them.
  
  
  
• Here's chest two:
  Head back to the top of the tower and jump towards the top of the shop to land on this rock. Keep going forwards. You'll drop down towards the end, turn left, and see a mouse near a campfire. The chest is to the back.
  
  
  
• Here's chest three:
  Again, head back to the top of the tower. There will be a patch of grassy land you'll jump to. Proceed forward, passing the second tree you see and slightly turning left till you drop down to another grassy patch of land. The chest will be near the base of a tree to your right.
  

Hopefully this was somewhat helpful for ya'll! Have fun in Atlyss <3