Well, it might be that the criteria for being a 'good woman' are overly strict or idealized in the story, making it hard to find someone who meets those standards. Also, the characters' own biases and limited perspectives could contribute to the difficulty.
A good woman being hard to find in a short story could result from complex character dynamics and social circumstances. Maybe there's a lack of opportunities for women to showcase their goodness, or there are external pressures that prevent them from being recognized as such.