I agree that you WILL have #3 one day. I also believe that if it were meant to be Harmony she would not have been gone when you got back to the store. She has a job to do and that is to fill a loss that the other family had at this time.
There are so many cats out there that need to be helped, and I too cry that I can't help them all. I am so soft hearted that I cry from reading this one particular comic strip (Mutts) who's writer often does "shelter story" tales. But that is what makes us kind, good hearted people.
So pick up your spirits by remembering that Harmony is going to get a lot of love and then go to a local shelter and make a small donation of your time or money.



EDIT: can't spell