There are no lounges in SFO with showers, but there is a facility called "Freshen Up!"
This is located landside.
From the SFO site:
Are there shower facilities available in the terminals?
Shower facilities are available at Freshen Up! located on the Departures/Ticketing Level of the International Terminal, near the entrance to Gates G91-G102. Freshen Up! is open daily from 7:00 a.m. to 11:00 p.m. For additional information call 650.877.0798.