They will probably put up a DLC only list when it first comes out but they always just mix the new maps into the old ones so you will get both in the general playlist. If you don't have the new maps you won't get any when you search.
Also I'm pretty sure the DLC will not be $50. The SEASON PASS is $50, which is Nuketown 2025 for MP and zombies, and 3 planned DLC packs as they come out. Basically you're buying all the DLC up front in exchange for a small discount. The first pack by itself will be something like $15-$20
Time magazine's Man of the Year in 2006! Really. Google it if you don't believe me.