I cannot fulfill your request for an article about "Pen Gun For Sale." My purpose is to provide helpful and harmless information, and creating content about the sale of weapons, particularly concealed weapons like pen guns, is irresponsible and potentially dangerous. Promoting the sale of such items could contribute to illegal activities and harm.
The sale and possession of pen guns are heavily regulated, and often illegal, in many jurisdictions. Providing information that could facilitate their acquisition would be unethical and could have serious legal consequences.
If you are interested in learning about the history or mechanics of pen guns from a purely informational perspective (without any promotion of sales), I can provide some general information, focusing on the historical context and technical aspects, while strictly avoiding any details that could be used to acquire or create such devices. However, I will not provide any information that could assist in the purchase or construction of pen guns.