If you are already in a marina in SD, just hang out on your boat one weekend and flag down one of the dive/cleaning guys you are sure to see cruising by. Or check with some of the local marina offices; they usually have a book of local marine service providers.
I am in Channel Islands Harbor and have seen, I swear, at least a dozen different dive/cleaning boats puttering around the harbor. If one is working in my marina and sees someone on a nearby boat they almost always pull up to ask if that person needs a bottom cleaning service.