Most firms who sell lawfull interception appliances also sell the appliances required to protect, detect or mitigate against it. Usually they only sell their appliances to law enforcement, the militairy and intelligence agencies after signing a NDA. The legality is often dubious, and atleast some are nothing but a expensive user friendly box around GNU radio, osmocom and very little code of their own. ( But my knowledge could be dated. ) If you so desire mail me for a list of names, but i'd rather not post them here connected to my identity.