Roman cheese is an Italian cheese named on behalf of "Rome". Pecornio Romano is quite tangy, sharp and salty and is made from sheep's milk. Caprino is even more sharp in flavor and is made with goat's milk. Vacchino is a mild version made with cow's milk. The U.S. many versions of "Romano" tends to be made from cow's milk and considerably more mild than the imported cheeses.
You can purchase some version of Romano cheese in most well-stocked grocery stores including Trader Joe's. Any type of Romano will add a nice sharp and salty flavor.
If you don't have Romano cheese then use one of these substitutes: