You can search for a casita-like dwelling under "Exterior Features" in connectMLS™. The selections that could represent a casita dwelling are Detached Quarters, Additional Dwelling and Garage Apartment. 

We have also recently launched a new field, Other Structures where you will be able to find a variety of structures related to the property. Some related options for a Casita-like dwelling are selected below.  

If you are interested in looking for an additional living space that is attached to the main dwelling, you can search under "Interior." The selections that could represent an additional living space could be found under Guest Suite or Maid's Quarters.