For my '65 Powermatic bandsaw, I stripped it down to bare iron, then primed it with some leftover Dupont 615 S Variprime 2-part zinc primer (the green stuff used on aircraft parts and bare steel) 2-part self etching. Anyhoo, that gave a solid base for a top coat.
For that, the closest match I could find locally was a quart of some off the shelf Ace Hardware store brand "Machine and Implement Rust Stop" Enamel. 

It sprayed on well and is pretty tough.

Since you are going grey (I assume), there should be plenty of off the shelf paints.
For about the best off the shelf protection, I always go for the spray cans of epoxy paint. Limited color pallet and takes a day to dry to touch, but hard like glass (and glossy if it matters).