Kontagion

There is a vendor right outside the tower that Khadgar is in that sells replacement rings, and rings for any other spec you would play.

I'm not sure if it was intentional by Blizzard or not, but at completion of Tackling Teron'gor, I was able to do the next step and acquire my ilvl 680 ring without completion of Draenor's Secret Power. It also needs to be noted under the "Preparing for Chapter II" section that you can obtain the Legacy of the Sorcerer Kings quest upon attaining the 680 ring, and that follower missions can give you a very early head start on collecting them. On an topic unrelated to content. In final considerations, Legendary is missing the y.

It's all dependent on the socket bonus. If the bonus is worth going for (normally 120 str), then it is best to use orange (str/crit) gems in red sockets, and crit gems in yellow sockets. Blue sockets can be tricky, if you can get away with reforging out of the extra hit rating, pick up the green (crit/hit/) gems in blue. If a bonus is less than ~60-80 str (don't remember the exact number, but I can get it for you later if you'd like), then gem all yellow gems. A bigger concern, is that at 504, you should not be prioritizing crit rating yet. Haste is a much more valuable stat until a higher

As far as items go, I would try to use the thok trinket instead of rooks, and alter gemming/reforging in order to stay around 9-10k mastery and the rest into parry and dodge, with more emphasis on parry. A higher avoidance build will give you a higher crit chance through riposte, coupled with the thok trinket which increases the damage of crits, your dps should definitely increase. You can always use the DPS legendary cloak as well.