We sourced these glass inlays from http://correllglassstudio.com/ in Conway, Massachusetts, not far from our office. They are known as bullseye glass and are cut into usable square panels from handblown rondels. Most hot glass studios can produce these; there may be one near you. They are also available online from several makers; search "bullseye glass" or perhaps "rondel glass." Thanks for checking in with us! Good luck with your projects.

Thank you.