There's many quests where you can get them :
"~Jungle Menace= It is possible to get monster bone+ from this quest, but it is a very rare reward.(I would say around 10-15% chance of getting one.)
~Attack of the Yian Kut-ku= Same as above, only around 25-30% chance instead.
~Catch a Yian Kut-ku= This is probably the easiest and best quest to get multiple monster bone+. I would say its about a 60% chance to get one in the reward and a 40-50% chance to get more than one.
~Catch a Gypceros= This is slightly harder than a Kut-ku, but will give 1-4 monster bone+ in the reward and a slightly better chance of getting them.
~Trouble in the Swamp= Same as above except: only 1-2 monster bone+ and less chance of getting them."
Simply writing "monster bone+" in Google search gave me an answer, why couldn't you have done it yourself?