I found him to be a bit annoying to find, possibly because I was doing Hand-me-downs at the same time as Military Breakthrough. For Hand-me-downs, you're retrieving items from dead guys in the mine field, near the quest givers. I continued on down into the ruins, because there were other Spitelash mobs visible from there. They're all level 15 mobs, running about in groups of 3 - generally a spellcaster & 2 fighters. As a trio, they hit hard & fast - at least for a level 13 troll druid. LOL
However.......
Warlord Krillian isn't down there; he's on the ridge overlooking the mine field from the other side of the mine field. He's up on a ledge overlooking the field, with 2-3 spellcasters ranged around him. He's an easy level 13 kill. Don't forget to grab the quest item, on the ground next to him. Of note, if you run up after someone else has killed him, you can still loot the item, then kill him when he respawns.
So in this case, knowing he was at 27,51-ish wasn't terribly helpful; that's why I've posted this additional more descriptive post, in case anyone else is having the same issues as I did.