Both Kodak and Fuji used to make, and probably still do, "slide duplicating film" which comes in 100ft bulk rolls, and is low contrast, intended to make copies of slides, so the copies are normal contrast. This is normal E-6 process film. In other words, if you use "slide duplicating film" your copies will be very close in quality to your originals. I used to use a small dichroic color head, inverted as a light source, and I could dial in color adjustment filtration to "improve" my original slides. I used a Nikon SLR with a macro lens on a copy stand as the copy camera.