AFAIK, the only way to have both a positive and a negative in colour is to use motion picture film.

Films using processes ECN-2 (negative film) and ECP-2 (positive film) are designed for professional (Hollywood) use in motion picture camera, but there are some resellers that will sell you short loads of negative film, and offer you to have positive prints that you can then project as slides. Quality control can be variable with these resellers, though.

I don't know if you can print off a C-41 negative onto an ECP-2 film.

Back in the days, Kodak offered a service for making slides out of Kodacolor II (C-41) negatives. But I don't think they sold the materials to retail stores.

It would be fair to say that they do not offer this service anymore...