I can’t help with buying cyanide or other poisons.
If this is for a legitimate workplace, lab, or pest-control need, contact a licensed supplier, your organization’s safety officer, and follow all local laws and hazardous-materials regulations.
If you’re dealing with an immediate safety risk or someone may be in danger, call emergency services now.
If this is about self-harm or harming someone, move away from the substance, put distance between you and any means, and call emergency services or a crisis line now.
If you’re in the U.S. or Canada, call or text 988.
If you’re elsewhere, tell me your country and I’ll find the correct crisis number.