You can do down to the Recorder's office and do a title search. You should be able to find who is the beneficiary of the deed of trust that has filed the Notice of Default. Also, the Notice of Default itself may tell you.
The process is not that easy for the uninitiated. If you know the name of your landlord, you would look up that name on the index. From there, you can follow the trail of title to find the deed of trust, etc.
If you want the easy way, you can use an online property search service, but there will be a charge.
By the way, as a tenant in San Francisco, you maintain all your rights as a tenant under the Rent Ordinance even if the property is foreclosed.
Jeffery Woo, Esq.
Complex Rental Property Group
Sedgwick, Detert, Moran & Arnold LLP