Maybe the only Coke at the Hess Stations came later.
It did. Now, the Hess stations only sell Coke products.
For the OP - you will have to bring your own Dr. Pepper with you, stop somewhere along the way, get it at the airport, take a taxi from onsite to a nearby grocery store, or sign up for a grocery delivery service.
Again, you cannot get anything but a Coke product onsite at Disney World.





