Considering there is a second season coming, I imagine HBO will put one out, though it might take a little while. Six Feet Under still only has one season set out. If HBO is smart they'll release a Carnivale set in time to build buzz before the second season starts up.
Carnivale is one of my favourite shows I'm waiting to buy this. I've heard from a messageboard the other day that someone said their husband worked for HBO and it comes out in November. I'm hoping it's true. Here's what they said. But I don't know if I can trust it.