Law enforcement officers can obtain information with a [search warrant](https://www.law.cornell.edu/wex/search_warrant), which is a document issued by a judge or magistrate that authorizes them to search for specific information or evidence based on "probable cause" to believe that it will inform the investigation or prosecution of a crime.

A court can also issue a [subpoena](https://en.wikipedia.org/wiki/Subpoena) at the request of a party to a proceeding before it.  Since in most cases only the state can bring criminal charges before a court, an individual would have to bring a civil complaint before a court in order to even request a subpoena related to his complaint.  Also, it is up to the court to enforce its subpoenas: It's not like a warrant where you can then pursue the items subpoenaed through force.  If the subject of a subpoena doesn't respond you have to ask the court to compel the party, which means you have to bring your complaint before a court that has jurisdiction over the party you wish to subpoena.