Another option - tho not a pleasant one to think about - is to go to the 
pound and request your tissue from them when they have to euthanize animals. 
One of my co-workers resorted to this at the suggestion of our pathologist.
I remember making quick friends with the medical examiner who promised to 
deliver "young" organs and one Saturday nite he made good on his promise and 
left me a gift of several lymph nodes and spinal cord.
Andi
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