the shareholders cannot have a subpoena issued. Shareholders have no rights to intervene in a corporate action. Can you imagine the legal quicksand if the courts allowed any shareholder of any corporation to take actions in a lawsuit where the corporation is a party? They couldn't hire enough judges or build big enough courthouses.
Under the law a corporation is its own legal entity or person with all rights to sue and be sued. When the corporation is sued the individual shareholders are not brought into the lawsuit. No one would ever own stock if they took on that responsibility.
Hope you did not pay your attorney for this advice. LOL
If you want subpoena rights you will have to file your own NEW lawsuit against the parties you want information from. AND you must have a cause of action before you will ever get information without the subpoena being quashed.