I have two large blackboards in my own office in Phnom Penh. I couldn't live without them. There is a shop that makes them out of wood. They aren't nearly as nice as a proper ceramic coated steel chalkboard (they still make these in china -- look it up on alibaba) but wood still does the job. The only problem is that it's difficult to find large chalk sticks. Couldn't find them in Cambodia or Thailand, but there is a shop in Vientiane (the capital of Laos) that bought a crate of buckets of multi colored sidewalk chalk years ago, and I'm the only one who buys it. I've now bought at least 10 buckets. The only problem is that there are only two white sticks in each bucket and Vientiane is very far from Phnom Penh.... sigh.