Certain individuals (like myself) have direct contact with personnel in various Departments/Divisions/Agencies, etc. who have direct and indirect access to radios on such systems and can run decoder software such as Unitrunker, DSD+, Pro96Com. This helps with identifying talkgroups, whether in the clear, partially encrypted, or full time encrypted to be submitted to the database for others to benefit and to listen with their ears (though some listen with their mouth it seems like).
As far as OPRA requests on the various radio systems, that's considered classified info and you won't really get too far with that in NJ. You'll get as far as what's listed in the FCC database, and that's about it.