ya, well for four horns, you need to bring a water attribute weapon (weakness) sonic bombs, barrel bombs and friends (if you have any)
weapon:i would recommend frost edge, but make sure to bring plenty of whetstones, coz it has rubbish sharpness.
sonic bombs: bring 10, and also stuff to combine them (gunpower and screamer) then throw them just after he dissapears under ground. it will get him stuck in something similar to getting a kut ku stuck in a pitfall trap. BEWARE. you cant do this when it is raging
Bring barrel bombs, sml and lrg to place down we he is stuck from sonics. bring stuff to combine them as well (gunpower and sml/lrg barrel)
as for monster bone +, you can get them from any HR 2 up monster.
otherwise, you can do a **** mission in the guild, where you have to kill a blue kut ku. you sometimes get one in the reward, or you can trade a smlbluekutkuear with the elder in forest and hills.
Also (almost done now) the storm of the yian kut ku, where you have to go into an arena and kill as many kut ku as you can, you can get monster bone + in the rewards there, depending on the number of kut ku you kill.
so, er...ya. hope i helped!