Don't think they had a splitter? They was a optional rs accessory you could order (different to rs models)

Have you thought about making a reproduction rs500 one fit or maybe a repo rouse splitter. The shape of the bumper isn't too different from a Cossie so should be fairly easy.

Or how about a Laguna splitter, used to see them on everything years ago, just bend to shape, screw on then cut off excess.