http://www.theruststore.com/Evapo-Rust-C21.aspx
I am using this with great success on some less-than-fine pieces. The problem, as with all chemical rust removers is that it leave the metal a bit grey and then you need to lightly sand.
It also may clean too deep and get into the patina, but if you soak a short time and then wpie, you can control that.
It also shows hardened metal as much darker. Not a substitute for vinegar, lime, lemon, etc.
I made a good sword "soak tank" by capping one end of a three foot piece of PVC pipe and hanging it vertically.
I like WD-40 and 400 grit to begin with. Watch your fingers, especially with these bloodthirsty Moro weapons!