look for "mastiha" or "mastic tears" and it might also be available in powdered form.
Mastic (Closeup)
From Nancy Gaifyllia, former About.com Guide
In Greek: mastiha, μάστιχα, pronounced MAHS-teeh-hah. At the market (continued below)
Gum Mastic
Photo © Jim StanfieldMore About Greek Spices
Full List of Spices with Greek Names and PronunciationGreek Herbs and Spices
More Greek Food Photo Galleries
Also from About.com:
©2012 About.com. All rights reserved.
A part of The New York Times Company.