PPG makes a product in quarts called "Flexed N Flat". You have to use a lot of it but you add it into the clear (of course). Works but if you ever need to touch up a spot it's HARD to match the flatness. And like I said, you have to use a LOT of it to get flat, or there is eggshell and then semi gloss. Gotta be careful using it or else it will look like little cracks in it or if you ever look at a desert ground or such where it hasn't rained in a long time it has little squares all over with cracks, it looks like that. If you decide to go with gloss black then check out SPI basecoat black or their single stage.
www.southernpolyurethanes.com
Barry is the owner there and VERY helpful when it comes to needing it and customer service is top notch. Maybe you already know of it, I know that some members here know of it and are on their forums. Hell, ask the question over there, they will know of a lot of different brands to use that are good and actually work well.