You can make your own chalkboard paint. There are several recipes online, most of them consist of the same ingredients:
1. A good quality FLAT latex wall paint (ANY color)
2. UN-SANDED tile grout (light for lighter colors, dark for darker)
The blending ratio is about 1 Cup of paint to 2 TBSP of un-sanded tile grout. Make sure you blend it WELL; break up any clumps until smooth. Put at least 3 coats down- in different directions with each layer and be sure to sand each layer LIGHTLY with 150 grit sandpaper when dry.
Season the chalkboard with the side of a piece of chalk, wipe clean with a barely damp sponge and you're set to go!
This is a nice cheap alternative to the store bought chalkboard paint which can be VERY expensive when you're painting large areas and you can make any color you'd like.
If you're having trouble with "lines" in the paint, you might try adding a TINY bit of water to the latex base as the paint may be a bit too thick.
Hope this helps!
( Magnetic Chalkboard Paint )