It’s called “Pit Fighter” in pvp, but it’s basically a Karma armor set available from Kessex Hills, Gendarran Fields, Field of Ruin, Lornar’s Pass and Harathi Hinterlands. The set called “Pit Fighter” in PvE is different and only available from zone completion rewards from lvl 70+ onwards (which you can find in the TP as well, the karma set can’t be sold there). All karma vendor sets can be seen at http://imageshack.us/a/img821/1415/karmavendorarmors.jpg
This is the PvE pit fighter set: http://www.gw2armor.com/human/male/named/heavy/front.jpg
And yes, you can transmute any heavy armor skin onto any other heavy armor, except those not available to your race (Cultural armor). You just need different types of transmutation stones, depending on whether any of the armor pieces are lvl 1-79, or 80 (the “regular” green stones and the “fine” blue stones respectively).
