I understand that the 'size' of the paintbrush has been released, atleast its designation. I don't recall now what it was, perhaps "size 5".
However, I believe that such a designation would relate to the size of the bristles, not the length of the handled.
I'm fairly certain that a local art supply store would be likely to stock only a few such brushes, so its lengthy might be surmized from what is locally available for purchase.