Rygarius posted on the forums early this morning that all conquest vendors have been disabled until a bug is fixed. The bug in question allows players to exceed the conquest hard cap, amassing over 2,200 points. In general it's not a good idea to exploit bugs like this, as Blizzard has been known to roll back achievements and gear at the least, and even suspend the accounts of the worst offenders. For instance the folks who decide to spam trade chat encouraging people to exploit a problem -- it's pretty easy to ban them.
There's no indication of when the conquest gear will be turned back on -- but given the high visibility of the problem it has to be near the top of Blizzard's priority list. We'll update when the vendors are back.