allen + roth Danish Limestone Gray 12-in x 24-in Matte Porcelain Stone Look Floor and Wall Tile (1.94-sq. ft/ Piece) in the Tile department at Lowes.com
Montclair Aged French Limestone Flooring - Historic Decorative Materials, a division of Pavé Tile, Wood & Stone, Inc.
Raw Gray Limestone, Sedimentary Rock Specimen - Approx. 1" - Geologist Selected & Hand Processed - Great for Science Classrooms - Eisco Labs: Amazon.com: Industrial & Scientific