[Quiet Man Cometh]

You always get one from the boss and there is often one or two hidden away in dungeons. You probably found them as treasure somewhere. Can't recall the map immediately off the top of my head but there are some areas where you need to go through a couple round a bout paths to get to them. Your map will usually give you an idea of where you can go but can sometimes be annoying to read if stuff is layered or pathways are above one another.

As annoying as it can be to fine ones way around, I've found that doing it yourself rather than using a guide makes it easier in the long run as you learn your way around.