It's going to be hard, because proceedings before ALJs are not always taken before a court reporter and the rulings are rarely published, at least in my experience before the California PUC. I would call the office of the head counsel for the administrative agency involved, for example, the California Public Utilities Commission, to ask whether there are publicly-available and searchable records of decisions. Someone in the agency's office of the general counsel (or whatever they call it) should know and probably would be helpful.
Another possibility would be to search for the ALJ's name in a legal data base such as WestLaw, to see if any of that ALJ's decisions had ever been involved in an appellate case.
