My textures came from some spherical environmental pics and a 3D graphics app. These images are generally produced by photographing a reflection in a mirrored sphere. That's how movie CGs do it too. That image was unwrapped to a rectangular image.
I sphere mapped that onto a sphere in a 3D graphic app, and rendered 90 degree FOV square images from a camera in the centre for each of the 6 directions. That produced the cubemap. I also added a table model with a GI rendered illumination map applied which appears in the spherical map and looked a lot better than a bright red carpet when the objects were sat on a grey table!
I sphere mapped that onto a sphere in a 3D graphic app, and rendered 90 degree FOV square images from a camera in the centre for each of the 6 directions. That produced the cubemap. I also added a table model with a GI rendered illumination map applied which appears in the spherical map and looked a lot better than a bright red carpet when the objects were sat on a grey table!