There isn't a whole lot of ways to get them, any wyvern (cephadrome and up) you kill, you will get a few of them in the reward box, that's how i always got mine.. sorry i can't be more helpful

~ Decado

you have to Capture he kut-ku, if you kill it, not much chance you'll have it

weaken it, then cut peices off its head
~keenan chung

1.you can barter it with machalite ore in forest and hills area...
2.I got many by killing yian kut-ku use bowgun and go to area 3 where velociprey and 1
vespoid inside.. killed all the monster, then wait for kut-ku.. you can kill it without
wasting your health..^^

in the cephalos or cephadome quest kill round spike tail donosauers if dosn't work abandon
quest and try again

if you get any med monster don't abandon quest either die 3 times or finish the quest

slay the yian kut-ku over and over at the end of the mission you get median bones,
screamers and a few kut-ku pieces like a shell, scale, or webbing

u can get it by carve it on apceros after u kill it at desert zone

In quest where fight yian kut yu. It should appear in reward. Like slay the yian kut yu
and catch the yian kut yu and they found in reward. Its easy kill too its easy way :p