If you don't have Molten Scream, whether normal or heroic, Lightning Rod is a really good weapon to pick up. Just to give you an idea, I think my guild started working on heroics the 2nd week of DS and we just had our first Dragonfire Orb drop last week. I think that's roughly 10 weeks or so. Dragonfire Orb is the best dps off-hand available right now, if you're luck enough to see it drop and get it, otherwise the off-hands listed above are your best options.
Somehow for my DS "Main" runs and, the orb does not drop. In my Alts runs, the orb drop and won by my Alt Moonkin =/. If only Blizz made the Orb as BoE than there's still an outside chance to buy it likely with crazy price but at least still obtainable.