In SF you could go to Marmot Mountain Works (Berkeley), Any Mountain (Marin) and REI (Berkeley is best).
In Seattle: Pro Mountain Sports, Marmot Mountain Works, REI (main store), though there are many others as well.
One other idea: you can call La Sportiva and they usually provide good guidance over the phone and you can order their mountaineering boots from them by phone as well. Be sure that you talk to someone knowledgable there if you decide to go that route. They also have a good web site:
http://www.sportiva.com/