Yes they sell them seperatly .. how do you think they are going to make money?? sell em together!?
Yes coraline algae is good, but you are really really putting the cart before the horse. Theres nothing in your system that can deplete your CA at this juncture from what I understand. Be patient my friend and buy a few books on this, something dated 1998 or newer would be best. Like the Consciencious Aqwuariast, or one that is older but still rocks, Baensch Marine Atlas vol. 1 or the newest I know out there, Delbeeks and Sprungs Reef Aquarium vol. 3. All are great reading and could get you a bit more knowledgable.
It is best if you grab and Alk and CA test kit, soon you will see you don't need anything right away. Or you should be able to just take a sample of your water to your LFS and have them test it for you.