catlad, hi
Yes they do exist, used by some Rifle and Shotgun enthusiasts but they are banned from use in competitions, because it would be possible for the competitor to have a "Spotter" using a radio with a receiver in the Headphones to give advice to the competitor, an absolutely bizarre concept, BUT?
As for where to get them, they should be available on shooting web sites, one of the guys I target shoot with, please note I am specific about "Target" and not game or any animal for that matter! has and uses [he does not compete at that level] but I do not know what these type of defenders are called, sorry about that.
As above they do exist and should be available on shooting web sites?
if you have no luck on such sites I can get a name but it will be next Thursday night before I am shooting with the person who has a set of such defenders just post and I will get the name for you.
Ken.