Where can I find an Iron bo staff?
As the others have said, that would negate the usefulness of the weapon. I have seen a staff that had the ends inlaid and capped with some steel, but it wasn't that much, and it did add some significant weight.
A bo made of iron will be quite heavy and almost impossible to use in a Martial Arts activity
That is called a quarter staff, not a bo staff. It's a mideviel weapon. And training with a weigthed staff or bar is a good way to tear all kinds of muscles and ligaments if you don't know what you are doing.
