Needle Works in Austin, Texas has a category called "Stitch Guides" in its online catalogue. It looks like all these canvases have a stitch guide included in the price. A nice touch is that in many cases you are told who wrote the stitch guide. I place mail orders through Needle Works occasionally and their customer service is always superb.
By the way, they do custom stitch guides. The rules are here but basically, you will be asked to buy the threads they recommend with the guide they write for you if you bought the canvas from them. If you didn't, you will have to buy the threads and pay $10/page for the guide.
Here is a listing of their current canvases with stitch guides. Currently there are 173 for sale, which means a nice little selection if you want to browse.
Stitch guide writers include Christina Arredondo, Amy Bunger (Amy's Keeping Me in Stitches), Susan Burris, Colleen Church (she's the owner of Needle Works), Cindy Howland, Kathy Kulesza, Carole Lake, Sandra Reddell and Cindy White. Since most of these folks have taught at Needle Works, these guides are probably not available elsewhere since they are probably former class items. I'm just guessing, but don't waste a lot of time trying to find anything except the Amy Bunger ones elsewhere.
The only other shop I know of that lists all its canvases with stitch guides in a separate category is Needlepoint.com. Here's the link--