Sometimes, developing new products or services is too important to be left to the same small portion of the company. That's what Will Raap, founder of the Gardeners' Supply Co., a mail-order gardening business based in Burlington, Vt., is discovering. The company, which had 1995 sales of $25 million, used to go through only the normal channels to find new products, says Raap. To get a fresh perspective, Raap asked five employees from various nonbuying departments--all expert gardeners--to develop a line of gardening products. The group, with full-time buyers as advisers, is spending eight hours a week for six months on the project. Some of its new products have already made it into the catalog.