Not factory. The Magnaport guns that contender mentioned were Super Blackhawks and were post-factory, They made a few hundred of each of several variants tied to different large African animals (I seem to recall seeing a Cape Buffalo version), and a few other editions. They sold them in wood presentation cases with a Magnaport logo on the lid and a patch inside, and maybe other items.
A 6" .357 seems an odd choice to port. When I was a teenager, I had a 6.5" model 29 ported and I ended up getting rid of it because I got tired of constantly cleaning the soot off the red front sight insert.
I agree with WMG, I have not seen or even heard of a FACTORY produced/sold ported Six Series revolver. I have seen them but all were post factory work contracted by the owner. Why? I have no idea. I've shot numerous, different loads (wimpy to Hercules+) and really didn't see the need to port the Six series (but I am a bit larger than the average person).
I believe some SP101s were sent to Magnaport from the factory and then sold by Ruger. Without the original packaging, it would be hard to tell. On the web site ser. no. look up, this one comes back as simply model 5718.