I don't know, (and I don't know if anyone would), but I've always assumed that he came up w/ those categories himself. It's not difficult to imagine him collecting moral imperatives from various cultures over a period of time, then reviewing them and sorting them by commonly encountered themes, and giving those themes titles. (At least, I can imagine that's how I would do it, if I were trying to create a similar illustration for an Appendix.) If Lewis wasn't the one who did that, I imagine someone else used a similar process.
However, since he often seemed to be careful to give credit whenever he used ideas of others, and especially in his more academic works such as _The Discarded Image_ or _Studies in Words_, I suspect that the lack of crediting another means we can reasonably assume this Appendix is Lewis' work.
Does anyone out there know any more?