Where? I know Iran, but where else?
Your local butchers.
If you have enough cash, anything is for sale....everywhere
No, I think not. There is a "black market" for that, from I've heard and read, and I believe it opens up an opportunity for some very unethical actions and dealings.
Legally? I suspect this already happens in a roundabout way, we just don't see it out in the open.
I don't know if selling them on the open market is such a great idea. But if someone wants to donate to someone specific and be compensated for it, I don't think they should be forbidden.