Actually, I just saw one for sale on GunBroker from this guy: http://www.noconeetrader.com/
In his description, he said that the NYPD ordered some of these and then backed out. Less than 100 were made and they were sold on the civilian market. I don't recall the model #, but it was definitely exactly like a Model 58 but in .44 Magnum. This guy knows his Smiths and this one had a factory letter with this explanation.