I've had good luck and like Walmart Colorplace primers and paints, but basically it only comes in NASA colors-- white and black... LOL
Yes, the auto supply is the best choice for the better quality spray paints like Duplicolor... Industrial supply houses like Grainger, Fastenal, and of course ag supply stores like Tractor Supply, Big R, and Rural King also carry pretty good selections of spray paints, usually in a fairly broad palette of colors for things like farm equipment (every brand pretty much uses all the different colors of the rainbow so to speak, and many shortline manufacturers also use their own colors as well, and they usually carry a pretty good selection of colors for things like trailers and smaller machinery and equipment that folks want to paint, or painting home-made or shop-built projects...
Don't overlook the auto-body shop refinishing suppliers as well... There's usually some shops around that sell various paints and materials to local body shops and stuff, and they can usually mix practically ANY color your heart could ever desire, in quantities from about a pint on up. Of course the cost can be quite high, depending on the actual formulation of the paint and the materials involved... but they usually carry some "bargain" formulations for shops building or repairing heavy duty machinery or trailers or stuff like that, where the paint is going to eventually get messed up anyway, so a high-dollar high-quality finish isn't really worth the expense... A lot of these autobody suppliers also may have surplus left over paints in various colors, some of which may be appealing to you for a project, usually in various amounts, and usually some of the higher end stuff, in varying quantities, and usually at a pretty good discount... If the painter has some left over of a high-dollar paint that might run close to $1,000 bucks a gallon, there's a lot of incentive to bring in a spare pint or two and sell it if he can get some of his money back...
Of course, this isn't going to be in a spray bomb (rattle can). BUT, ask at the supply house if they have a "PreVal" sprayer... it's basically a little jar that screws onto the bottom of a can of propellant, into which you put the paint. The paint is drawn up by a straw into the spray nozzle by the propellant when you press the button, basically identical to a spray can... You can use this with the automotive bulk paint pretty easily, and for small projects its adequate... but if you're getting into bigger projects, or want to paint all your rockets this way, you might want to look into getting a secondhand compressor from a garage sale or craigslist or something (avoid the cheap "oilless" compressors if you can-- those have a pretty limited lifetime, and I'd NEVER buy a used oilless type, because it's probably on the way out, which is why they're selling it). I'd highly recommend a small portable belt-driven compressor (with an electric motor, which turns a compressor with a piston and small crankshaft operating in oil), which is more than adequate for an airbrush, will do fine with a detail (small) spray gun, and can even be used with a larger spray gun if you give it time to recharge and "keep up" with the air demands of a larger gun. A small compressor and airbrush can be had fairly cheaply, and you can use pretty much anything you want at that point... plus it's easy to "scale up" later if you want-- Harbor Freight has perfectly adequate 'detail guns' (small spray guns) for about $20 bucks, as well as small pressure regulator and air dryers (combined) for about the same... I have both myself-- an HVLP gun and a Harbor Freight air dryer/pressure regulator that I use for painting farm machinery... wouldn't paint a show car with it, but for farm machinery, trailers, even older vehicles, it's the berries... It would CERTAINLY be adequate for any rocketry project you could think of...
Of course for sheer convenience, rattle cans are hard to beat...
Good luck! OL JR
