As one of the larger online shops, Needlenook of La Jolla has a nice search function. You can go to their main catalogue, then put "stitch guide" in the Search tab on the right to see what canvases with stitch guides they have available. Some stitch guides are extra, some are included with the canvas at no extra charge. Read each listing you are interested in with care to discover which category the guide you want is in.
The shop also has a custom stitch guide service for canvases purchased from the shop. Costs range from $35-$125 depending on the size and complexity of the design. I don't know who does the guides but David McCaskill manages the store and does lovely guides.