They were introduced in The Burning Crusade to give freshly dinged characters a fighting chance in pvp. You could purchase these items by becoming honoured with the correct faction, and this was not too difficult a challenge because as you leveled (whether through questing or dungeons) by the time you hit level 70 you would have had the rep to buy a few bits of these pvp sets.
The factions that you need honoured with to buy these items are;
Honor Hold - Alliance/Thrallmar - Horde
Keepers Of Time
If you don't have the rep, at level 85 it is very easy to just run through the dungeons (more rep for heroic I think) and you might even pick up some other gear for transmogging.