The only thing that is per-day is the lockout for choosing a specific heroic. You can repeat it on normal to farm the rep up. I did this with NL for highmountain yesterday and today I am in the process of doing it with maw for valarjar.
I farmed 8k rep with HM last night, gets tiring.
Just went Neltharion normal again, and still no drop. :/ Seems like either it's on some form of daily lockout or a low drop chance.
warlocks look like they've got to be exalted with any 2 factions, possibly excluding nightfallen.
so far that's consistent with the people who have gotten bindings (remember someone was HM/nightfallen exalted i think)
So I heard the other binding drops off Ash'golm in the Vault of the Wardens. I cannot confirm though.