The bow is not a common drop. Guard Nobunaga is not a common pop, and if you are lucky on spawn you chances to get bow are 1 in 6 if I remember and PH vs Guard is 1 in 6 so do the math. I have gone 20 straight PH before name has popped.
Guard Nobunaga & PH are located on top of stairs. Spawn time for PH is 19 min : 45 sec
Bow itself is okay but it procs at level one. In PvP this is big. Hitting a low level for 100 hurts.
Good Luck Farming.