I have found 3 chalkboard paint recipe methods, one with non-sanded grout and some other ingredients, one with baking soda and cornstarch, and one with only paint and baking soda. I have included them from different websites I found.
Chalkboard Paint with Baking Soda
Make Chalkboard Paint with Non-sanded Grout
Make Chalkboard Paint with Cornstarch
I will have to try some of these soon...until then,