Heat the oven to 120C fan or 140C conventional and line some baking trays with baking paper. In a large bowl, stir together the oats, puffed rice, puffed buckwheat, cocoa powder and salt. Heat the honey and maple syrup in a pot on low until it begins to bubble, then turn off the heat. Pour the honey mixture over the oat mixture and mix with your hands until everything is coated. Spread the mixture onto the baking trays and bake for about 45 minutes, turning the cereal every 15 minutes so it doesn't burn. It is done when crispy. Let the cereal cool completely before storing in jars.