Barbarian Lord Oogga one day bashed in the skull of a mage and then decreed
'GO FORTH AND TRAIN'. Several of his warchiefs decided that they had best go
teach others the ways of barbarians.
You may find these trainers near mountains, not too distant from the major
continental cities (excepting Shadowkeep). However, one must demonstrate one's
true barbaric worth to Oogga in order to move up the ranks in the guild.
(i.e. the 'advance' command is not available).