Buy fresh dungeness crab in Tomales Bay / Point Reyes area
Years ago Tony's in Marshall cooked crabs daily...I don't know whether they still do on the few days they are open. I don't frequent Tomales Bay much any more, but I don't recall any "crabs off the boat" on Tomales Bay. Bodega Bay is your best bet. We had some Bodega crab last night and they were very small (1 to 1 1/2 lb) and rather tasteless. I can't say why, but they just had no flavor at all.
Do you want live raw or fresh cooked?
We used to buy it at the Marshall Store, which was fresh and well-cooked, i.e. not funky tasting from not changing the cooking water, and not overcooked. The last time we did it, they'd had an ownership change and didn't really know how to ring up a whole crab for us, and it was super expensive. Given the convenience, it might be worth stopping in and having a trial baloon crab cocktail, then buying whole crabs if it's good and the staff doesn't rub you wrong.
There are a few other places along highway 1 where you'll see a spray painted sign that says "crab" when they have it.
If you get lucky on the timing, you can often buy fresh live crab at the docks all along the coast. I've gotten it in Bolinas direct from the fisherman, and I'm sure you could do the same up in Marshall, but it really requires lucking out with calm weather for the previous 24+ hours so the fishermen can go out, set their pots, and then retrieve them. If the swell is over a few feet, they won't usually go out.
Up in Bodega Bay, there's a harbor phone you can call to see what fish is available. It's a long, though gorgeous, drive north from Marshall.
19225 Hwy 1, Marshall, CA 94940