This quest, and the chain that leads to it, is only available to players that choose to build the gladiator arena in Gorgrond, instead of the lumber yard.
In order to open this quest up you need to first complete a long list of other quests (below). Rexxar will not appear in the location on the map until you have completed these quests (as I found out the hard way). Note that Chains of Iron is for the acquisition of a garrison follower! [npc=85278]
Sorry this is so long but it took me forever to get this information, as I chose to build the lumber yard and haven't leveled any alts yet. I looked forever for this quest, only to find out I can't get it, and I want to make sure this info is shared, thoroughly, with everyone who may need it.
Rage and Wisdom (5 quest chain)
Horde - Rage and Wisdom
Alliance - Rage and Wisdom
Seedbearers of Bad News
Horde - Seedbearers of Bad News
Alliance - Seedbearers of Bad News
A Harsh Reminder
Horde - A Harsh Reminder
Alliance - A Harsh Reminder
We have Company
Horde - We Have Company
Alliance - We Have Company
Cauterizing Wounds
Both factions - Cauterizing Wounds
On the Mend
Both factions - On the Mend
Complete Basilisk Butcher, available for both factions - Basilisk Butcher
Complete Is This One of Yours?
Horde - Is This One of Yours?
Alliance - Is This One of Yours?
Horde - What the Bony Xuk? - What the Bony Xuk?
Alliance - The Crystal Shard - The Crystal Shard
Horde - Xuk Me, Right? - Shells for Xuk
Alliance - Hard Shell - Hard Shell
If you want to, you can skip right down to - Bad at Breaking - Bad at Breaking but you will have to continue the chain anyway. I am not sure it matters if you do the faction specific quests first or not.
Both factions - Nisha's Vengeance - Nisha's Vengeance
Both factions - The Gronn Strategy - The Gronn Strategy
Horde - Xuk it - Xuk It!
Alliance- What's Under There? - What's Under There?
Both factions - Fair Warning - Fair Warning
Leave Every Soldier Behind
Horde - Leave Every Soldier Behind
Alliance - Leave Every Soldier Behind
Both factions - A great Escape - A Great Escape
You may also have to complete Down the Goren Hole - Down the Goren Hole
And Will of the Genesaur - Will of the Genesaur
before getting the next required quest.
Both factions - Eye in the Sky - Eye in the Sky
And that should open up Chains of Iron.