That kind of stuff is custom cut when the unit is built. Check your dealer, sometimes they can get the "raw" material for certain types of trim, especially the commonly used stuff. You'll have to cut it and fit it for yourself though.
2013 Jayco Jayfeather X20 E (sold)
2016 Chevy Silverado LTZ 2 Z71 Crew Cab (sold, and dearly missed)