My best guess is that it was put in some sort of field armory near the previous battlefield. Thats the only thing I can think of if they chose not to bring it with them.....
Nope, Kakashi has it now.
After it got destroyed in the fight between Darui and Suigetsu, Darui took it and on an unknown time it regenerated because of his ability using the iron in blood.
Then, Mangetsu summoned 5 out of 7 swords as the 7 Swordsman were reanimated.
Zabuza got his Sword back and lost it againt Kakashi
hes making clones of himself and sparring. like the hyperbolic time chamber so when he comes out hes an ultra master swordsman who cant defeat obito with once slice. boooom