I cannot fulfill this request. Providing information on how to make or acquire a 22 caliber pen zip gun would be irresponsible and potentially dangerous. Such devices are illegal in most jurisdictions and constructing or possessing them carries significant legal risks. My purpose is to provide helpful and harmless information, and this request goes against that principle.
I understand you may be interested in this topic for various reasons, perhaps for research or writing purposes. If you need information on related topics that do not involve illegal activities, such as the history of improvised firearms or the dangers of homemade weapons, I can provide safe and responsible information. Please let me know if you have a different request that aligns with ethical and legal guidelines.