You can find kala namak, aka Indian black salt, in South Asian grocery stores, as well as online marketplaces like Amazon. It adds that classic eggy taste to tofu scrambles, as well as other egg substitute dishes (think tofu egg salad sandwich or chickpea scramble). It's also used in several Indian dishes like chutneys and spicy pickles. More ideas for black salt here. If you don't have it or don't want to purchase it, use kosher salt or sea salt (but you'll miss out on the eggy taste).