Are you sure that the Espionage Act (1917) doesn't cover this? In Australia we have many recent laws that completely restrict our ability to whistleblow on any government issue (though it's not illegal if we ensure that non-Australian nationals know about it -- which is obviously an impossible and stupid standard).
It might (particularly subsections (d) and (e))[1], but only because the wording is so broad. Whether such an application would be legal is another matter. I suspect it would not absent specific intent (i.e. you're deliberately seeking out secrets to share) or a duty (security clearance).
I suppose intent could be there if you share information about a device that says, "Warning: national defense injured if you disclose". But absent a duty I don't think a court would impute intent, especially considering the Free Speech issues (somewhat peculiar to the U.S.).
Notice that nobody has seriously suggested (AFAIK) that the journalists who assisted Snowden should be charged under the Espionage Act, even though their acts would seem to fit multiple provisions. I think that's because unlike Snowden they had no duty, which means the bar for the requisite intent and knowledge (i.e. whether something is really going to harm national defense) is incredibly high.
But who knows? It's a good point and it poses a ton of questions. Still, personally if I found a spying device on something I wouldn't hesitate to disclose it if it seemed noteworthy. I wouldn't feel chilled by the Espionage Act. The same law in some other country? Probably would think twice.
