There are quite a few accessible spots around Monterey and Carmel bays in California. Spearfishing won't be the best, but you will probably hit good visibility and there are sites in the bays that will be more protected than the coastal sites when seas are up. Spearfishing for rockfish and lingcod is open in California year round.
I was going to suggest Ocean Cove along the Sonoma Coast, but it's a private campground that's closed over the winter. Salt Point Park, just north of there, has good diving at Gerstle Cove (so I've heard). Stillwater Cove just south is another spot.
Noyo harbor in Ft. Bragg (stop at SubSurface Progression dive shop first to ask about sites), and Albion campground south of there, are possible access points with a kayak or inflatable, conditions permitting. There aren't all that many spots where access is close enough to the road - and not down a cliff - for shore entry or portable boat launch. There are other access spots around Ft. Bragg as well.
Lawson's Landing at the mouth of Tomales Bay is another option when conditions permit, and has camping.