What kind of paint are you using? Burnt Sienna is a close match to a canvasback head and straight burnt sienna will do the trick well for gunners without mixing. If you were using artists oils or acrylics, finding burnt sienna would be simple. In fact, you can go to any art store and find a tube of it. If you're using latex house paint, I have no idea (probably something weird like Dried Toucan Blood).
If you want to paint in oils, for v-boards I think that Ronan's Japan Colors would be perfect. It dries very quickly, and very flat. That comes in a can. As far as tube oils go, the world is your oyster. I've used Grumbacher's with good sucess. It dries much slower, and not as flat.
I don't use acrylics, but Golden's is popular.
You could probably find some automotive primer in a spray can that looks like the color of rust and get away with it, too! Just err on the side of brown, not red.
I hope this helps.
Mike
