I'd check the resources available in each state in which you will be traveling through and need routing. Many have online resources as well as printed materials. Nearly every state publishes a bicycle map of some sort that they will send out for free and the bicycle/pedestrian coordinators often have more information they can distribute for no charge as well. And while the maps aren't as detailed as ours, they generally offer suggested roads for cycling through their state. Here is a link to the contact information for all of the bicycle coordinators and some online materials: http://www.pedbikeinfo.org/data/state.cfm
For more tips and ideas on how to create your own route, see this blog post on the topic:http://www.adventurecycling.org/resources/blog/how-to-create-your-own-route/
Good luck and have a great tour!