Unless they changed this, the lead of the 3 group packs is a 100% drop for Xzomit organs.
The trick that many use is to Sleepga them by zone, kill the lead, get the organ, and then zone. The "hard" part is to cast Sleepga on them as they "swim" on past (rather rapidly). You don't need to worry about Sleepga hitting the 'Hpemde's since they don't aggro unless you actually do damage to them.