Where to get information on June 22 1974 shooting death of Charlie Gray in Miami Florida?

Probably the best thing to do is to research the archives of the the leading Miami newspaper(s) of the time, or contact their research department directly and request assistance. Remember! You are referring to a case that is now 35 years old. Unless the case is still open and part of the active "cold cases" of the Miami PD or Dade County SO, most of these records will have been 'retired' to storage somewhere.