Well I don’t know about texture but I can tell you how to create a real location heightmap .First you need to sigh in to NASA’s Earthdata. They will provide you with user id and password.Then select the option GDEx (LP DAAC) from Data Discovery menu to get your heightmap .But, u need a image editor to convert jpeg to png .This surely works.I have used it a lot of times .Have a good day G.riderello.
There is a register option so first register.
https://urs.earthdata.nasa.gov/