Google: Packit Gourmet, Just Tomatoes, Harmony House, Carolina Shelf Reliance. All these come in small as well as large packages. Packit Gourmet will even prepare your own custom meals if you want. There are others. Trailcooking.com has many sources (go to the very end of "Links and Resources") and lots of other information about preparing food for the trail, including lots of recipes using supermarket ingredients. You can also cook up and dehydrate your own stuff.

Many health food stores, including Whole Foods and some health food departments of Kroger and other supermarket chains carry small packages of the "Just Tomatoes" brand fruits and veggies. You can also find interesting stuff in the bulk bins there.