I use a works connection glide plate on the CR500AFs no troubles.
(as well as carbon fibre glide plates)
and while i havnt tried fitting one up on a KX500AF,.,.
i believe any "glide plate" style made for a KXF450 would fit well,
at least any of the carbon fibre or alum ones..likely would
however
a more coverage, /wider skid plate might need trimmed i nsome areas .. to fit.