I used to buy this rub already made from a local Middle Eastern market, however, now that I know what Kamil uses, I make my own. I still however, get the sumac from him. It is optional if you don't have access to a market such as this one.
There are countless versions of this particular spice mixture. Feel free to adapt to your own tastes. I did.
1 t garlic powder
1/2 t sumac
1/2 t salt
1/4 t cinnamon
1/4 t cumin
1/4 t black pepper
1/8 t allspice
1/8 t cayenne
Mix spices in a container with a tight fitting lid.
When getting ready to use, add about 1 t of spice blend to olive oil and fresh lemon juice as the base for a marinade. Taste and adjust as desired.