Local Police statistics from the Bureau of Justice Statistics (BJS). You will also have to search the BJS site using the terms "Profile of local police" or "profile of local law enforcement." There is no one report that compiles data for the entirety of the last 40+ years.
Statista - Quantitative data on over 80,000 topics from 18,000 sources. Has current data on police force demographics, and more.
"Law Enforcement" section of the Characteristics of the Criminal Justice Systems in the Sourcebook of Criminal Justice Statistics. These reports only give data for large city police forces and state law enforcement agencies back to 1990.
In the search box provided on each website, search for the specific type of surveillance equipment (ex., body cameras, in-car cameras, etc.) for which you would like statistics.