Any old skull won’t do – we’re just rather picky about the elegant curve to the brow ridge on these skulls. Crafting is delicate work. Only the Sayer knows how I’m turning spruce planks into a yew longbow (which is shorter than a shortbow).
Jokes aside, I agree with your comment about scarcity. Bear paws, bear skulls, wolf skulls and a handful of others are crafting/upgrading bottlenecks. In multiplayer foes don’t seem to drop more of these, foe numbers aren’t much higher, and everyone needs the same items around the same point, exacerbating the shortage.
That said, I think you’re especially unlucky or speaking hyperbolically. The droprates are 27% or 43% according to data exports (could be outdated), so the chances of no skull after 20 kills are below 0.185%. I do get a bear skull roughly half the time, bears are just very rare. Crafting a bunch of bear items for a specific facet is rough.
Overly long further thoughts
This may be by design, as farming means replayed content and oberabundance means having everything immediately. In multiplayer we bandied about some ideas like taking on a bounty to slay some juiced-up bears with a reward of bonus paws/skulls at the end. We’ve also noticed that lower-tier mats end up in large stockpiles before long, so maybe when T4 to T6 are released bear and wolf mats will be abundant.
Irmgard can trade up mats but comes online only at the end of the current experience. Pure speculation, but maybe she’s a stopgap due to T3 being the end for now.
Some items have no recourse. I wanted to try a plagued bow and couldn’t get a facet or gem to save my life for a week despite checking stores, Finley, Seneschal, and fishing actively. Grabbed the spell from shroudcleaver in the end.
On the other hand I have hundreds of unused items of some types (mostly consumables and raw ingredients), to the point I dunk them in whispers or campfires or sell stacks for copper or have to construct storage ’cause I can’t hold all these mushrooms.
Maybe these could be thrown into a recycling recipe, ideally one that generates more gameplay, like donating them to the city to generate targeted bounties.