Use PPG DX 520. It is a phosphoric acid based coating chemical (easy to work with using regular latex gloves, if any) that will produce a zinc phosphate coating on galvanized or steel surfaces. Bead blast the parts first, soak them in the DX 520 solution for about 10 minutes or until they have reached the level of color you want and then remove from the solution, dip in water to neutralize the process, blow off with an air gun to dry, and coat with a thin coat of WD-40 type oil (unless your painting them and then just prime or paint right over the phosphate). DX 520 can be purchased at your PPG paint store. I've been using this method for years on my nuts, bolts, suspension parts, on my resotrations. Even if I'm going to paint a small part, I will phosphate coat it first because it protectects it from corrosion while I'm waiting to paint.