It just depends on how big you want them.  the commercially available cover
slides (used by biology departments) are very cheap and typically 0.1-0.13
mm.

They can be thinned very easily too (the largest size I'd used  was 2cm X
2cm thinned to 50 microns).

>I am looking for a supply of rectangular glass sheet of 0.1mm thickness.
>Can anyone suggest a source of such material.
>
>Thanks
>
>Joseph Cefai
>
>