Tahini is a ground sesame seed paste, similar to peanut butter. It is a creamy, oily, and smooth nut butter rich in calcium. Look for tahini in a glass jar or a can, and sometimes in a powdered, dehydrated form in health food stores, or in the ethnic foods aisle of your regular grocery store. You can also find fresh tahini in the refrigerator section next to the hummus in larger well-stocked grocery stores.  From:  About.com

Tahini in a Jar – Sold on Amazon.com in the grocery section.