I looked it up in Red Eagle News Exchange (RENE), which is a Ruger reference. There were only 3 stainless guns made in the 10.5" barrel, Model KBNM-10, S/N 600-00123, 600-00124, and 600-00125. 3 more were serial numbered but there is no known reference. So if you have one of these six guns, you have a gold mine. Actually, S/N 123 is known to be in a private collection. S/N 124 and 125 were retained by Ruger.
So for all practical purposes, there weren't any stainless guns available to the general public, but they did make a few.