Where can I get Potassium Cyanide?

The best answer I have seen to this often asked question is

"If you have to ask this question, you almost certainly won't be able to get any!"

Medical shops do not sell deadly poisons .. what human use is that! You don't tell us which country you are in ...so we can't answer anyway ...... most countries have strict laws about selling deadly poisons.

If you need it for a genuine experiment, you'd could get it from the lab where you are going to do the experiment. No one who is in their right mind would use it anywhere else. You haven't mentioned anything about ordering any antidote as no sane person would use this without ording the antidote to be standing by .. just in case.

There are educational supply stores out there that you'll have to find yourself, but it is readily available, if you have the correct authorization to use it.