San Francisco Snow Cones
I'm not sure if there are places that call it a snow cone (or Sno-Cone?), but there are lots of places that sell shave ice -- May's in Japantown comes to mind but I think other places in Japantown and Hawaiian restaurants are your best bets. Many bubble tea parlors such as Tapioca Express sell very snow-cone-ish drinks in a huge variety of flavors, and some may even sell shave ice. For the finest in shave ice, go to Shuei-Do in San Jose Japantown, but they won't sell it until the summer.
May's Coffee Shop
1737 Post St Ste 395, San Francisco, CA 94115
Shuei-Do Manju Shop
217 Jackson St, San Jose, CA