I'll attempt to answer my own question: I searched a remote-control-codes database and believe that the code is 1869, although I have not been able to verify that as I don't own a universal remote that will accept that code. However, I did purchase an L5 infrared remote accessory for my iPhone and I created a remote with codes for both the Rio Central as well as the empeg/Rio Car remote and uploaded them to the server available as public domain. So if you own an iPhone with an L5 I believe you can download and modify these remotes. And finally, I was able to procure a remote from replacementremotes.com in case anyone else needs one.