A walk through the Greek casinos on ChipGuide reveals that only 2 of them used the Greek Key (Large Key) mold on some of their chips. Here's a sample of 1 chip from those 2 casinos: Club Alexander and Casino Mont Parnes. (Chip pics courtesy of MoGH/ChipGuide, of course.)

Alas, both were located on land-based Athens. If one had been on a Greek island, I was hoping to use the homonym pun "Greek cay", but such is not the case.