I suspect your dealer might be your best option. After all, he would have to order one from somewhere if a new trailer came in with damage.
OTOH, if you need a non-standard size, a cabinet shop might be your best bet. Matching the color could be a problem.
Perhaps a picture framing shop could tack you together a frame and you could fill in the middle with whatever.
Happy Camping! ///// Richard D.
2006 4x4 Ford 250 SD / 2007 Flagstaff 827 FLS
One very patient wife and one furry child who travels with us. Forty-two years of trailering and camping, and I still have a blast.