A question about a recipe: A Medley of Roasted Potatoes with Homemade Za'atar & Aleppo Pepper

It is easy to make yourself--it's a spice blend--but Penzey's carries it, in addition to the Middle Eastern stores already suggested.

Here in Jerusalem -- it's referred to as "thyme", but it's a mixture of thyme and sumac, and depending on who's making it, usually oregano. But -- not always. It's in just about everything, but the 'normal' way of using it is to sprinkle some on a plate next to a pool of olive oil, tear off a piece of whatever (good) bread you're eating, dunk the bread in the olive oil, and then into the za'atar. I'll be leaving here in a couple of months, and while it may be a long while before I crave hummus, tahina and/or za'atar, I never tire of the flavors. Good stuff.

That roasted potato recipe lists the recipe for the za'atar. But if you can't make it yourself, any Meditarranean or Middle Eastern food market will carry their version of za'atar.