I've never had two harissas that are the same: I'm quite fond of what Pita Inn serves: lots of garlic, it's very close to a Mexican salsa.
I have bought two different ones from specialty stores, and I'm happy with neither. The first was extremely bitter and I threw it away.
The second has the texture of a tomato paste, and some flavors I can't quite place but probably includes caraway (based on recipes I've seen online).
You can probably get away with a red salsa that's more oriented toward chile than tomato/onion. A thicker hot sauce might do.
I just checked a couple cookbooks:
"The Arab Table" by May S. Bsisu (a teriffic book, by the way), merely says, "Harissa is a hot red sauce from Morocco and Tunisa, used as a condiment in many North African dishes. There are several variations of the sauce, but my favorite is the simple blend of sun-dried chiles, garlic and olive oil. Some other combinations include cumin, coriander, mint and caraway."
"A Season in Morocco - A Culinary Journey" by Meera Freeman (a better coffee-table photo book than a cookbook) has a recipe that is pretty much as simple as above, blending
fresh red chiles, salt, lemon juice, vinegar and olive oil.
What is patriotism, but the love of good things we ate in our childhood?
-- Lin Yutang