I got spray cans of Krylon Ultra Flat Black for my scopes from an auto supply place but it was some years ago now. It is often used as a camouflage paint for hunting etc. as well so may be in these type shops too.
It is a bit blacker than chalkboard paint but you can just use that instead.
Textured flocking (like protostar) will absorb more light than both. If using in a newt tube then the area opposite the focuser is the most important bit to make absorb light.
BTW - check this article out:
http://www.cloudynights.com/item.php?item_id=85