The Kenwood KCA-R6A can be found easily online through
google, for instance
here
It doesn't have all the features of the Rio remote (all longpress options etc), but it's the closest thing to the real deal - used to come with the MkI (and IIRC with the MkII).
Differences can be checked out in the
Button Guide, and
here
Edit: Regarding the sled - your fastest, simplest and cheapest option is probably to find someone local to you that knows how to solder - the harness is not very hard to work on (compared to some of the internall SMD stuff...). Info on how it is wired can be found
here and
here.
/Michael