Within the Crime in the United States report from the FBI, one can find police employee data by status (sworn/civilian), among many other statistics.
However, national data on shootings by police is not collected: "The nation's leading law enforcement agency collects vast amounts of information on crime nationwide, but missing from this clearinghouse are statistics on where, how often, and under what circumstances police use deadly force. In fact, no one anywhere comprehensively tracks the most significant act police can do in the line of duty: take a life.
"'We don't have a mandate to do that,' said William Carr, an FBI spokesman in Washington, D.C. 'It would take a request from Congress for us to collect that data.'
"Congress, it seems, hasn't asked."