Chalk finish paint can be purchased at most common stores where regular--or any other kind--paint can be found. This includes Walmart, Lowes, and The Home Depot.
Similarly, chalk paint can be made, or purchased from online studio websites such as Royal Design Studios, or Etsy. There are also websites like Pinterest with good tutorials on how to make good quality chalk paint.
For clarification, chalk finish paint is a paint that has a chalky finish comparable to matte, but even less glossy. Chalk finish paint is commonly used on furniture, and other accessory items, to create a unique, antique finish.