You might check with Sherwin Williams paint stores to see what they can mix in their industrial enamels.
Single stage and 2 stage normally refers to catalyzed urethane automotive paints. Single stage being basically the same as clear but with color added. 2 stage refers to painting first with a base coat which is the color and then topping with clear urethane.
Obviously, automotive paints offer the widest range of colors. But, for the type projects you mention, they're generally cost prohibitive. A pint of paint can cost anywhere from $100 to $300, depending on color. Urethane grade thinner goes for $65 to $85 per gallon. Activators are similarly expensive, and have very poor shelf life once opened.
Then there's the level of protective equipment necessary for spraying any catalyzed paint, including hardware store enamel to which a hardener has been added. Paint suit, full face respirator or air supplied hood. Isocyanates are much like Covid. You might get by with nothing more than minor irritation, or you might end up dead. So, when someone comes along and claims they've sprayed 500 gallons of Imron with a shop rag tied around their head, you can listen to that advice at your own peril.
I've painted several cars on a hobby basis, and have all the necessary ppe, but, for small non auto projects, I use rattle cans or a brush. Or, once in a while I'll spray some straight enamel for something larger like a piece of lawn furniture, but it's just too much aggravation to get suited up and set up to safely spray small amounts of catalyzed paint.
As others have mentioned, there's a wide array of colors available in spray cans, but you won't find it at dollar general for 2 bucks a can.
