Lowes and Home depot have some decent soil mixes, usually time released, stay away from those unless you're knowledgeable on the time released nutes. Are you referring to soil mixes? Or actual plant food additives such as magnesium etc? Look in the How to section in the growers part of this forum, it has a ton of information to point you in the right direction. Doing your homework first is essential to producing high quality meds, except the lucky ones who somehow throw a seed in the ground and yield incredible amounts... haha.
P.S. Here's the link, it's an excellent compilation of information on everything from start to finish for your grow. 420 Magazine ®