The game's collection data lists Rubbery Fish Head as sold by a vendor NPC in Valdrakken.
Vendor
Zone
Map
Waypoint
Other items it sells
NPC #199599
Valdrakken
-
-
792
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 12.0.7.68887 (Midnight (patch 12.0.7)).
Blizzard numbers items as they are created, so the named items next to ID 199896 (199891 to 199902) were usually added in the same batch as Rubbery Fish Head: the same quest line, zone, vendor or reward set.