Re: 445 Super Magnum
Unfortunately, I know of no commercial source of loaded .445SM ammunition. It is possible that one of the small custom loaders (Buffalo Bore, etc.) may produce it, and might be worth searching out.
Yes, it's possible to shoot .44 Special and Magnum loads in the gun, although my experience is that the Specials aren't terribly accurate. Both shorter rounds foul the chambers badly, and require a good cleaning before using .445 ammunition. Dan Wesson didn't endorse the practice.
Hope this helps!