Harissa is a chili pepper paste from North Africa. It contains roasted red peppers, serrano peppers, spices like caraway, coriander & cumin, as well as garlic. I would think you could easily substitute sriracha or any other hot pepper sauce you have on hand. But you will want to experiment with the amount of hot sauce you use. The harissa paste has a kick, but isn’t quite as 5-alarm HOT as many ‘hot sauces’, so a Tablespoon of sriracha would probably be too much, compared to a Tablespoon of harissa.
Once the pandemic is over, I do encourage folks to seek out harissa though. Even boring old Kroger carries a few types, some thicker and darker and more pungent, some thinner and brighter and more spiced. I tried it because Blue Apron sent me a recipe that called for it, and even though I am a total baby about spicy foods, I fell head over heels in love with it. It’s got that flavorful spice, rather than purely ‘burn-a-hole-in-your-tongue’ fire that deadens your taste buds. 