I need to find one more to complete my full set of Barroth armor, but I for the life of me cannot find another one. I have killed Barroth 5 times, and captured him 2 times with no sign of that elusive bone. I wanted to have it so I could move on to Gobul but I said screw it and fought Gobul anyways since I here that he can drop Monster Bone L's as well, but he isn't dropping them either.
How can I get just 1 Monster Bone L relatively quick?
It's not that great of a solution (you might not even be able to do it at that point in the game), but sending the fishing boats out to the Distant Isle can sometimes land you a Monster Bone L or two. It's pretty much as much of a crapshoot as killing/capturing Barroth/Gobul over and over again for MBL, but at least the latter method gets you materials and zenny.