Jarred black bean sauce sold at Asian supermarkets, Chinese grocery stores, and some mainstream supermarkets can be substituted. Lee Kum Kee produces a spicy black bean sauce and a black bean garlic sauce which are both quite tasty. However, some black bean sauces can be very salty. I recommend try a little bit of the sauce to gauge how salty it is before adding any additional salt to the stir-fry.