For calcium oxalate, try Pizzolata'a method specific for the Ca Oxalate.

We would run a von Kossa and the Pizzolata, to help differentiate between
crystals in kidney of cats who drank antifreeze.  If you can access an
dog or cat kidney who has succumbed to this poisoning, you will have
a control for the oxalate.  Try a local veterinary diagnostic pathology
lab, they may be able to help you, I looked in my controls, alas, 
did not have one.  

The control was a tissue with Ca that would stain with von Kossa, and
the calcium oxalate, to provide elimination.  The Pixxolata is simple
and very nice, also look at sections with polarized light, if possible.

Gayle Callis