The clerk of a district court at the request of any party to a suit pending in his court which is brought under this subchapter shall issue a subpoena for any witness or witnesses who may be represented to reside within 100 miles of the courthouse of the county in which the suit is pending or who may be found within such distance at the time of trial. The clerk shall issue a separate subpoena and a copy thereof for each witness subpoenaed. When an action is pending in Travis County on the consent of the parties a subpoena may be issued for any witness or witnesses who may be represented to reside within 100 miles of the courthouse of a county in which the suit could otherwise have been brought or who may be found within such distance at the time of the trial.