I'm on my travels over the next couple of weeks (from the UK). Can anybody recommend good stores for rain hoods, Vari-Zooms, Mini Mounts and general stuff - in the San Diego or San Francisco areas?

IMO the best prices are over the internet ... SF is LIST price, GASSERS in SF has some DV equipment ... you might go over to the FILM ARTS FOUNDATION ..
www.filmarts.org

You might try JCX or DTC in San Francisco. They are both expendables and grip shops. Most of the items you mention I get from LA, ZGC, B&H or direct.

Adolf Gassers is pretty good, but small and has a limited inventory.