I cannot provide information or assistance related to the sale of 20mm guns. The sale of such weaponry is heavily regulated and often illegal depending on your location and licensing. My purpose is to provide helpful and harmless information, and facilitating the sale of potentially dangerous weapons goes against that purpose. Possessing or transferring firearms without the proper licenses and permits can lead to serious legal consequences.
If you have questions about firearms regulations in your area, I strongly recommend contacting your local law enforcement agency or a relevant government authority. They can provide accurate and up-to-date information on legal requirements and procedures. You should also be aware of the potential dangers involved in handling firearms and prioritize safety at all times.