There's a large, legal market for firearms in the US, so it's not hard for a criminal to take advantage of that. What's going to produce a large, legal market for dedicated gun obfuscating devices that criminals can similarly take advantage of? I don't think that there is going to be one. I think it will be more like a criminal getting access to e.g. plastic explosives: either he's part of a criminal organization, already has a specialized day job that allows for diversion, or has reasonably high technical skill and can manufacture the materials in a home workshop. I'm not sure the "diversion from legitimate business" path even works here, because again, I don't see the business need for disguising open carried guns. If Johnny Hothead, having no specialized connections, gets an offer to sell him some explosives then it's probably coming from an agent of law enforcement rather than the local Crime Depot.