I use Humbrol Matt Cote. For me the key to applying this, and I found this out the hard way, it to make damn sure the the stuff is mixed properly, and to apply it lean...
I've found that I can apply Testors Dullcote with a brush to small areas. I use a wide, flat brush, and I'm careful to minimize the amount of material that's in the brush, applying it with a stippling motion.