MARILYNN MARCHIONESome people who buy supplements to avoid Big Pharma drug companies may find themselves doing business with Big Herba, instead. Some of the same companies that mass-produce drugs in huge chemical labs also churn out vitamin and herbal pills sold in bottles with rainbows, sunrises and flowers on their labels. Dozens of other supplement makers reap more than $100 million in annual sales. One of the largest ¿ NBTY Inc., on New York's Long Island ¿ sold $2 billion last year in the United States alone. Its brands include Nature's Bounty, Vitamin World, Puritan's Pride and Sundown. "They used to be mom and pop operations but now they're major companies," said Bruce Silverglade, chief lawyer for the consumer group, Center for Science in the Public Interest. There are hundreds of small firms, including niche players with only a few products. But they account for a slim slice of total sales, industry experts say. Supplements often are sold through multilevel marketing ¿ distributors and franchise holders earn commissions by selling and recruiting others to sell for a large company at the top of the pyramid.