I've been trying to find a source of clear glass discs, around 35mm diameter and preferably 1.5 mm thick (though 2mm is OK). They are for the windows in optical toys so don't need to be of high optical quality. A local glass firm made some for me with a diamond core drill, but they are not very good - loads of chipping round the edges. A friendly glassblower did a much better job but I can't call in that favour too often. It's not so difficult to find precision optical windows at a price but I don't need that sort of quality. Google has turned up nothing, but there must be a supplier out there as commercial kits for e.g. kaleidoscopes have three in them.
Hopefully the collective wisdom of the groups may have an idea of a source? I only need about a dozen. All suggestions gratefully received.