Microscopy slides for projection?

[pathology at mscf.med.upenn.edu]

Can anyone tell me a supplier of glass slides whose size and thickness are
suitable for projection through a regular 35 millimeter slide projector?  Our
histology laboratory used to stock this item, which is used to make what
we call "whole mounts" of paraffin-embedded, stained tissues.  Our supplier no
long sells such slides.  Where can we buy these 2-1/4 by 2-1/4 inch 
slides now?  Thanks.

Gregg Wells
Department of Pathology
University of Pennsylvania
Philadelphia, PA  
email:  pathology at a1.mscf.upenn.edu