The game's collection data lists Regail's Crackling Dagger as sold by a vendor NPC in Warspear.
Vendor
Zone
Map
Waypoint
Other items it sells
NPC #88569
Warspear
-
-
166
Vendor NPC, zone and position come from the client's collection source tables (CollectableSourceInfo and CollectableSourceVendorSparse); coordinates are the in-game map readout.
Build history
First seen in build 5.5.4.69585 (Mists of Pandaria).
4 other items in the current build are also called Regail's Crackling Dagger. Same-name entries are usually a different rank, faction, quest stage or reward track of the same object.
Blizzard numbers items as they are created, so the named items next to ID 87152 (87147 to 87157) were usually added in the same batch as Regail's Crackling Dagger: the same quest line, zone, vendor or reward set.