Look for Cotija cheese in many well-stocked grocery stores as well as most Mexican markets. You can also purchase cotija online at Amazon.com:
El Mexicano Queso Cotija.
Cotija is also available, ground. Los Altos Cotija Mexican Cheese is aged, salty, and sharp conveniently ground to a finer texture for use in soups, pastas and moles or as a topping to some of your favorite pizzas, pastas and more. Queso Cotija Molido is available at Amazon.com