A specialistpaint distributor *should* be able to supply the correct primer....you could always look for Automotive paint and bodyshop suppliers on the Net, from there, find the manufacturers, such as Dupont, Sikkens Etc and email their tech.dept direct...they should have tech. sheets to cover prep and application.
Marine applications also come to mind.
Have you been looking at retail outlets for Professional "trade" paints?
You are obviously a capable person, determined to understand your machine and learn the disciplines needed to maintain it. Professional engineering suppliers are the way forward. I think you'll find Zinc Chromate primer available in 1/2 litrepacks upwards..generally, 2-pack paints are streets ahead of solvent, or water-based stuff Avery thin, translucent coat is all that's normally needed....again, a paint-manufacturer will give full details of systems , prep, different coats and overcoating etc. hth.