Finding Cases
One S.D. Cal. case references a promising case – In re Biovail Corp. Securities Litigation, but it's from S.D.N.Y. Let me keep digging...
Let me look at the Beaver County case from N.D. Cal. and the Harrington case which involves non-party subpoenas to investment funds:
Excellent! The case that most directly matches your criteria is Beaver County Employers Retirement Fund v. Tile Shop Holdings, Inc., No. 3:16-mc-80062 (N.D. Cal. Jun 7, 2016).
It involves a non-party short-seller (Gotham) being subpoenaed for trading records and sources related to a short report.
Facts
The underlying matter was a putative securities class action in the District of Minnesota. The plaintiffs filed suit after Gotham City Research, LLC—a non-party short seller—published a negative report about Tile Shop Holdings alleging undisclosed related-party relationships. Gotham had taken a short position in Tile Shop stock before issuing its report, and following the report’s publication, Tile Shop’s stock dropped 39%.