This achievement is tied exclusively to the in-game FEAT "Rule Southern Shara" http://teradatabase.net/us/achievement/285/
and you can use this website to find the location of each monster required. You can access the in-game feats by pressing start, going to character, then selecting feats. This specific feat is under Exploration>Southern Shara.
To complete this, there are 8 World Boss BAMs and 7 regular BAMs, and you only need to kill 1 of each.
The World Bosses have long respawn timers, so if you don't find it in the listed locations you can switch instances/channels. Press start > press Y > select any other channel > press B and wait for it to zone you automatically.
The regular BAMs are plentiful and have short respawn timers.
Thanks to Miss LunaFreya and GD Great Healer for pointing out the in-game feat and prompting this whole post.