Ironite is a retail product. Too costly for a big lawn. Look for a liquid iron product, Ferromec or something similar. The chelated forms are better and more expensive. And many types of iron will stain equipment and concrete, cheaper types worse.
My tests have shown that iron will give the turf a sort of black stain--you get a blackish green. And it only lasts as long as it takes to mow off the black-colored grass blades.