I collect Johnson, Cleveland, Keene and Diamond fareboxes and have never seen one of those marked as such. It looks very much like a shop-built box from Milwaukee making it a fairly rare item. Does it actually have a Johnson tag on it? Does it look like this - http://www.johnsonfarebox.com/fare44b.jpg that was taken from http://www.johnsonfarebox.com/gallery4.htm
I’d be really interested in seeing more pictures of it. All of my Johnson, Cleveland and Keene boxes (that were constructed with keys) have the Cleveland 4-way key. Some like the Johnson “J” did not have a key nor did many of the Johnson “D” or Reg Lock boxes.
Sorry I can’t help with the key and I wish you the best of luck in getting that sorted.