Easy to find truck stops on the interstate highways as a rule. It is on the secondary highways and out in more rural areas where diesel is harder to find. I have found gasbuddy to be worthless in the remote areas and don't even bother with it when traveling.
If you go to the websites for Love's, Flying J, Pilot, Exxon, Chevron, and others you will find locations that you will not find on gasbuddy and they will be current as to the availability of diesel at individual stations. I also use the yellowpages.com website and search by town for "diesel" and this is effective about two-thirds of the time.