Where to buy Toro
Try Niijiya Market in Japantown. They specialize in organic and high quality Japanese ingredients so I think their Toro should be up to snuff. The other place I would consider is Yummy Yummy Fish in Irving Street: they are Japanese fishmongers who sell fresh sushi grade fish daily as well as offering a small sushi bar to the rear of the establishment. Here are the contact details.
1737 Post St
San Francisco, CA
2. Yummy Yummy Fish
1015 Irving St
San Francisco, CA
re: david kaplan
Furthermore, since the ownership change last year, sadly, I wouldn't buy fish for sashimi from Yum Yum (see www.chowhound.com/topics/397287 for links to a couple of reports). I haven't braved the sushi since the change, but I did once go against my better judgement and buy a piece of salmon there that turned out to be clearly past its prime. The few times I've been in the area and poked my head in, the fish generally seems to be in that condition.
Supermarkets that sell sashimi more or less get their supplies from the same wholesalers as restaurants (e.g. there's a mention somewhere online that Suruki, Nijiya and even Todai buy from IMP whose Bay Area warehouse is in Hayward, though there are different grades of fish available), except restaurants arguably buy more in quantity and have access to the higher quality stuff that supermarkets might not (or not want to).
In addition, there are seasons where toro might be off, depending on which part of the world they came from or migrated to. I've no idea what wholesalers have to offer, but in speaking with one or two local sushi chefs, they do get blue fin from either Croatia, Mediterranean, even locally (probably nearer the seas towards Mexico that are arguably lower in quality) and hopefully in the season to come, Indian Ocean.
Nobody really knows where the toro comes from in the supermarkets, so it is all luck of the draw. I do agree that while Suruki is great that you can have sashimi cut to order, it can look off during frequent visits.
I'd check also with Nijiya Supermarkets (San Mateo, Mountain View) and perhaps the big Suruki supermarket in San Jose (280 @ Saratoga Ave) where I've usually seen pretty good looking marbled blue fin tuna belly though I've never tried it there (but have with Nijiya with ok results). There's also Tokyo Fish in East Bay and Berkeley Bowl (call in advance before you go).
The last resort, where also arguably would be a better guarantee for quality, would be to ask your favorite and hopefully befriended/trusted local sushi chef, and perhaps buy a small block from him directly at a bit of a markup, otherwise order toro sashimi to go and put it in an ice chest/cooler for transport.