i too have found around 5.....all have foreign coins except one is hollow, and its a 2-tailed kennedy...so it wasnt made to come apart, rather be used to always win in a coin flipping competition...keep searching, and you too will probably find some! keep it up and hh!
These are very common in coin tricks and one of the best tricks it is used for is called "Scotch and Soda." This hollowed out half has been around for a long time in the magic community and this is the first time I have ever heard of it being used as a "Secret" spy coin. I go with it being designed for the magic community and not the world of espionage.
There was a post a few months back on these and many members replied they had found them while CRH.