Yeah, I got mine off a player too. Personally I'd say that's where your luck will be. Just try to be inconspicous (sp?) in a huge battle and loot people.
Don't think mobs drop it. Just keep looting dead people, pray that you get into an AV where people are actually fighting instead of rushing drek. Which, never happens anymore sadly.
According to WoWhead, only 2 mobs are listed as dropping it, but they have an obscenely low droprate (like .3% or less), which probably indicates a false positive, or that the item no longer dropps off of any mobs at all.
Most likely the most reliable way to get it would be to be quick looting the corpses of the opposite faction.
On a side note, the tower achievement is quite easy to get as an alliance boomkin. horde like to stand on the outside of a tower, one little spell and they go flying off. Very nice to allow me to cap like that. So far the record is 4 times on someone falling for that same stunt. Luckily i got perfection ages ago back when you could still gave larger premades without going against a premade always.