Nothing that I know of built-in.
The solution you're looking for is in 3D math.
The simplest one I can think of is generating a random 3D vector, normalizing it, and then multiplying it by the sphere's radius. Then add the vector to the center position of the sphere, and it should be a point on the surface. I would test that though, that's just off the top of my head.
If it has to be something that matches some blocky sphere's collision bounds, then you may have to use a random raycast from center to find the surface point.