If a True Value doesn't stock XO-Rust in gallons or quarts, they can order it; just be aware they may need to order case lots (four cans per case). Now and then it comes up on sale, watch for a flyer....
Tractor Supply Co. (TSC) carries a good supply of tractor/implement paints. Not a huge selection of colors, but hey........Google them for a location near you, cool place! They do catalog too, IIRC!
Maybe Agway carries similar stuff, I don't know.....
Rustoleum is sold in quarts and gallons in many places, including Home Depot. HD usually also sells a 'house brand', but I'm not as happy with that as I am with Rustoleum.
Spray cans can be done, they just take forever, expensive. Pretty convenient, tho! Do a bit at a time; if you only have 15 minutes a day, it can be done! Just watch out you don't spray the neighbor's Mercedes by accident on windy days.
Again, watch for it on sale, and buy it by the case (6 to a case, you'll need LOTS of cans).
Many paints can use brush, roller, or spray. If using a roller, use a LOW NAP roller for the smooth surfaces, and be prepared to overbrush in spots with a hand brush.
Prep by scuffing the area with 3M pads, then wash with PLAIN (not scented) dish detergent and water. When fully dry, you can paint.
Treat rusty spots with POR-15 primer. Good clean metal uses brown primer.