Hunted for this blood all weekend. Killed every wolf at all 3 camps many times and only saw it drop off of sonic pups and sonic wolflings in the NorthEast section of zone when wolves control east cave.
There are 3 spots in the NorthEast section that they spawn that I know of.
First one is large lower area by Grimling forest zone. Either a sonic pup, wolfling, or sonic wolf will spawn.
I then ran to island between the 2 bridges and would find another, sometimes 2 would be there(think the extra one is Curfang's PH). Again either pup, wolfling, sonic wolf, or Curfang would be there.
Next I ran over to the area along the eastern zone edge just north of the eastern cave where the wolves are. Again, either a sonic wolf, pup, or wolfling would be here. Rinse and repeat.
Also, when wolves take over the Northern cave (normally owlbears), a pup, wolfling, wolf will spawn by Vah Shir fort but haven't got any to drop from them yet.
Hope this helps.
Edited, Mon Oct 6 12:48:44 2003