The ingredient Hound Tooth is collected from Skinned Hound corpses.
5 guaranteed samples can be found, in the following locations (magenta crosses on map):
Hound Teeth are obtained from most types of Skinned Hounds, including Greater Skinned Hounds. Hound Teeth do not come from Relmyna's (dead) Skinned Hound or from Ushnar's Skinned Hound. However, "Hound Corpses" (already-dead hounds) do yield Hound Teeth.
In most places, Skinned Hounds are generated by Undead and Wilderness leveled lists, which only spawn Skinned Hounds starting at level 4. Along the shorelines in Dementia, Skinned Hounds instead appear at levels 1 to 20.
Places where respawning Skinned Hounds can be found at all levels include (red and orange circles on map):