You might try contacting Riverpark Inc., they are a distributor of mobile electronics based in Elkhart IN. (big surprise!). RiverPark
They are a distributor of the Xite line and may be able to help with a remote. I do believe the remote was an "optional premium accessory" for units such as yours.
I did a lot of research on Senecas before I bought mine. I thought I might go used so I looked at the 2012 models-on. Ended up buying new, but my research time wasn't wasted.