Cover Glass (15mm diameter, for 24-Well Plate, 100/cs) [801007] - $35.00 : Bioland Scientific, for Your Research Needs
Hack for (more easily) extracting coverslips from 24-well plates : r/labrats
CELLTREAT 229172 15 mm Round Cover Glass, Fits 24 Well Plate, Sterile, 1.5 cm L, 0.02 cm H, 1.5 cm W, Glass (Pack of 100): Amazon.com: Industrial & Scientific