Finally, I have accumulated enough emblems of conquest to buy Evoker's Charm (19). However, getting from 19 to 25 emblems of conquest is taking longer than I expected. Probably due to we only manage to run Ulduar 25 intermittently.
Btw, the good news is PUG are getting familiar with Emalon nowadays, so minimum of 2 emblems of conquest per week become more achievable. Refer to here for list of conquest raiding gears for Warlock.
My next target is Breastplate of the Wayward Conqueror (58) which will take quite a while to get, may be should just wait until 3.2.
Note: in 3.2, emblems of conquest will be dropped in dungeons or raids that previously dropped Emblems of Heroism or Valor, such as Naxxramas or Heroic Halls of Stone.