UPDATE Found the small disposablecompostable litter pans at PetSmart fit perfectly. The cats use this with no issues, and its really great because it minimizes tracking! 

Its a sturdy and handsome-looking enclosure, it matches our powder room so well but....the major downside (and my own fault for not double checking) it is so small that Im having trouble finding any litter pan small enough to fit. This was purchased for our 2 cats and there is no way it is going to work  (