I couldn’t find chalkboards at Staples or Walmart, and instead of ordering online or looking at art stores, I just bought black heavy duty poster paper. It worked really well as a chalkboard, and the kids even washed it off repeatedly. Still can be used again later as well!
heavy poster paper, chalk pastels, water, wash cloths, water container, tape (for wall)
- draw
- wash
- repeat!
Christy M. King 
Chalkboards are so overrated anyway. I bought a few little ones for my students a while back, but some are higher quality than others and there is no real way to tell. I found out that they make chalkboard paint a while back, and we use that on wood sometimes.
We use tar paper at my school. It works just like heavy-duty poster board and it is totally waterproof, so you can leave it outside on an easel and just let the rain clean it. It doesn’t smell very good though…