Cold-and-flu season is here again, which means it's time to put Grandma on standby with a supply of chicken soup -- and to refresh one's stockpile of echinacea, vitamin C, and zinc. For one-stop shopping, nutritionist Oz Garcia suggests Whole Foods (2421 Broadway, at 89th Street, 212-874-4000; and 117 Prince Street, 212-982-1000). Author of The Balance and president of Personal Best, a nutritional-consulting firm, Garcia has sent many health-conscious Manhattan celebrities -- including Donna Karan and Veronica Webb -- to this nutritional emporium. "It's one of my favorite places on earth," he says. However, for especially hard-to-find supplements, Garcia recommends Hickey Chemists, Ltd. (888 Second Avenue, at 47th Street, 212-223-6333; and 1258 Third Avenue, at 72nd Street, 212-744-5944) or Willner Chemists (100 Park Avenue, at 41st Street, 212-682-2817; and 253 Broadway, at Murray Street, 212-791-0505). Both stores offer wide ranges of products as well as highly trained staff. When asked which store he prefers, Garcia grins and says, "That's like asking, 'Which Ferrari do you want?' "