With the introduction of Sunrise, General Mills Inc. may be the first major manufacturer of breakfast foods to enter the certified-organic cereal market. The cereal manufacturer says the idea to enter the market was borne three years ago in response to customer requests. Among the hurdles the company reported it had to overcome was locating a source of millions of pounds of certified-organic grains and other ingredients. In addition, the cereal must be manufactured, shipped, and stored in accordance with exacting standards. Sunrise was tested with consumers in the summer of 1997, underwent some tweaking, and was formally unveiled Mar. 12 at the Natural Products Expo West in Anaheim, Calif. It is certified organic by Oregon Tilth, an industry organization that sets and polices standards for organic products.