If it's wood finish trim that you're replacing, you may find the finish (or something close) at a building supply store. If it's the vinyl wrapped trim that matches the wallboard, then you may find it at Trekwood.com or possibly a Keystone RV dealer may have some in their parts department. Usually when a warranty repair is approved, Keystone will send that dealership the materials to complete the work. Often they'll send a 8' length of trim, even if the area only requires a shorter piece. Sometimes dealers throw the excess away, sometimes it gets stuck on a shelf until "spring cleaning". So, maybe you'll get lucky asking a dealer for any scraps, maybe not. It's worth a try if you're relatively close to a dealer.
2015 F250 6.7l 4x4
2014 Cougar X Lite 27RKS