Organic Valley Pasture Butter is produced seasonally but I can usually find it year round. It tastes great and is healthy, too, because of the high level of omega-3's etc. from the milk from pasture-grazing cows.
Raw dairy products can be difficult to find depending on your location. Here in the Bay Area, I know Organic Pastures makes a raw butter in a tub, which can be bought at Falletti Foods in San Francisco. If this isn't available, I'd say the Straus or Organic Valley brands are second best.