There is a website called Terrain Party, that actually allows you to select an area in the real world to export as a height map that will work in the engine.
World creator has a tutorial on using terrain party in part 3 of height maps tutorial. But this is of course using their software, but may still shed some light on terrain party.
Yup, I’v used it without any issues. Also, I have not found any other websites to get free height maps from yet, they are kind of difficult to find. Best bet is terrain party, or you’ll have to make your own. There is also the option of googling images of height maps but your options are going to be limited.