Slickshift is right. An epoxy paint will provide much greater protection than an alkyd paint.
I was thinking "inside the box" of only oil based and latex paints.
You might also want to consider a "moisture cure polyurethane", which are also generally considered industrial coatings. On of the biggest names in non-yellowing moisture cure polyurethanes is Wasser.
Maybe e-mail them and describe your problem, and they'll recommend a suitable product.
But be warned. These products are not inexpensive. You'll be looking at $150+ for a gallon of a moisture cure polyurethane paint. Check with Wasser as to the performance of moisture cure vs. epoxy paints on metal. I suspect one possible advantage the moisture cure might have is that you may be able to reseal the can if you don't use it all so that you can apply a second coat. However, I believe there would be enough humidity absorbed into the paint while it's open that resealing the can might not be feasible anyway. Check with Wasser on that.