The guys on the Yahoo group said that the Krylon ultraflat black (part of the camo series) is the flatest paint that they have found to buy. I haven't tried it yet. Several of them also suggested a milk paint, and they also said that to get a paint really flat, you have to mix in some kind of "crud" to make the surface rough. One person was using oregano leaves chopped, dried and mixed with the paint. There was something suggested, but I don't remember exactly what the compound was called.
I used the Krylon Camo on a firearm I painted and that stuff is like looking into the monolith orbiting Jupiter. It is absolutely flat. Have not tried it on a camera yet.