The closest one I found so far in a spray can is Rustoleum "Sail Blue"... it is not exact it is lighter than the Ford Blue but a wee bit darker than the Iseki Blue... If you are painting a whole part or parts that are not directly next too or touching the original paint, it is a pretty close match..... Ofcourse, like any paint job, if the original paint is faded or oxidized in any way, new paint, even if it was the original paint code will not match exactly...
Options, paint the entire tractor a new color of blue viz viz Ford NH Blue as done in the previous post... or take a part to your favorite body shop... many use spectrometers that will actually match the paint and can probably come reasonable close to the color.... Obviously, this will be more expensive than a $3.99 can of store bought paint..
Another option is to actually get the paint code from Iseki or an Iseki Dealer... It is quite possible Iseki is using a paint not made in Japan... Many folks in Asia use German paints......
Anyway, let us know if you come across another option...