What must I do for a black knight sword?

Also, I just killed a black knight while simultaneously dying (both delivered our killing blows at the same time). Is it possible that I may have lost whatever item they dropped or what?

Random drop sadly. Luckily its a common weapon choice, but its just luck.
I am pretty sure its gone, that svcks, but there are plenty of the guys to kill. Im sure you will get one of their weapons. I favour the helbard.

There's an area in the game with a lot of Black Knights (that aren't one-time enemies) (I won't say where in case you've not been there), but I'm fairly sure there's a Black Knight Sword wielding one there.

Also. Man-Serpent Greatsword. That is all.

Do we need a new thread?

And @ Seti: The very last area you visit, re-spawnable black knights that drop titanite chunks of all colors and any and all black knights weapons.

Post limit reached, time for a new thread.