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.