Need 3D Drawing in .stl Format for 3D Printing

The item that I would like to have printed out consists of three spheres [approximately 3.0” in diameter each] that partially intersect equally. The area of intersection amongst all three spheres is called the “Spherical Triangle” [or "ST"]. I would like to have each sphere printed out individually with the intersecting area missing from the spheres, as well as having the ST printed out separately so that you could put the four pieces together and pull them apart to illustrate the concept of the ST. Lastly, I would like to have a 2 piece case [Top/Bottom] printed that is solid except for a cavity that will allow the assembled spheres to be held in the case.