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;
The Sha'tar
Honor Hold - Alliance/Thrallmar - Horde
Cenarion Expedition
Keepers Of Time
Lower City
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.
